Last month, in a small party led by British Museum curator Jessica Harrison-Hall, I went in search of Chinese treasure 600 years old. The quest was made in advance of the forthcoming British Museum exhibition, Ming: 50 years that changed China, which is devoted to the beginning of the 1400s, a crucially formative half century in the nation's enduring idea of itself.  The tour took in museums and temples and historic sites in Beijing and Shanghai, Nanjing and Jinan; the treasures included dragon-embroidered silks and the finest gold jewellery; nine-masted ships and intricate, princely tomb relics – doll's house artefacts for the afterlife; scrolled calligraphy and – naturally – the peerless porcelain vases and vessels that are the headline acts of the early Ming era. Many of these objects will be leaving China for the first time for the London show, which opens next month. Collectively they represent a unique insight into the establishment of power and government in Beijing and beyond; they also, inevitably, cast light on the power and government of China's extraordinary present moment.  Having spent a good part of the past century attempting to erase "decadent" evidence of China's imperial history – some of the irreplaceable exhibits in the Ming show were rescued from the scrapheaps and landfill of the Cultural Revolution – the party leadership in Beijing has lately made the celebration of that history a national priority. In the five-year plan of 2011 the Central Committee announced that culture is the "spirit and soul of the nation", and would become a "pillar industry" – representing 5% of GDP. The plan dictated that China was to build up to a thousand new museums by 2015, a target already achieved.  Existing national and regional collections have been rehoused in vast marble halls. Private museums have been created to showcase the trappings of the newly minted elite. Liu Yiqian, for example, a cab driver before he discovered Shanghai's stock market and became a billionaire, bought the world's most expensive wine goblet – a Ming porcelain cup decorated with chickens – with his Amex card for £19.6m at Sotheby's in April and, having scandalised the curatorial community by drinking tea from it, will put it on display in his new £22m Long Museum. The repatriation of such items, as well as the industrial-scale excavation and recovery of Chinese history, represents a resurgence of national pride, but also a kind of national necessity – all the empty new museums need things to fill them.  This surreal expansion provides another perspective on the epic scale of China's ongoing reinvention (the five-year plan also legislated, for example, for the creation of 45,000km of new high-speed rail track to link the nation's major cities, much of which is already being constructed – HS2 might eventually provide about 400km). It was by high-speed rail that we travelled south from Beijing to Nanjing, on the Yangzte. The colossal rebuilt Nanjing Museum contains 100,000 items from the former imperial collection. Nanjing was the ancient capital of China, and it was there that the Ming dynasty was established in 1368. In those days the journey between capitals old and new took 20 days. It now takes under four hours.  That particular journey was emblematic of the changes of the early Ming (literally "brilliant" or "shining") period. Having overthrown the Mongol dynasty of the Yuan, the new ethnic Chinese emperor sought to live up to his own adopted name Hongwu, meaning "vast military power". To this end he created a society that supported an army of one million troops and established the navy's dockyards in Nanjing as the largest in the world. Those dockyards are in the process of a multimillion-pound excavation, and one huge pot-bellied Ming ship – then the cutting edge of naval technology – has been reconstructed, but little of the original remains.  To get a real sense of the power of the Hongwu emperor – who began adult life as a wandering beggar – you have to travel outside the city to his mausoleum. We visited near dusk; a light rain was falling on the newly recreated pavilion roof that houses a monumental stone stele erected and inscribed in his honour. The stele marks the entrance to the 2km Sacred Way, a wide road to the emperor's tomb guarded by pairs of enormous carved animals (including camels, lions, elephants then native to China) to ward off grave-robbers. A hundred thousand men built the mausoleum site and its walls over two decades. Jungly vegetation has encroached around the great tomb itself, a closely guarded secret for centuries, and you can now get a golf buggy along the Sacred Way, but the original sense of granitic and autocratic power remains intact.  Hongwu sought to spread that power to the four corners of his vast nation state by establishing the most capable of his 36 sons in regional power bases. He armed them with a set of written dynastic instructions concerning responsibility and filial duty. Some adhered to these tenets better than others. Zhu Tan, Prince Huang of Lu died aged 19 from the overdose of a drug he believed to be an elixir of eternal life. His tomb, excavated in recent decades with exquisite items preserved in the (new) Shandong regional museum and loaned to the London exhibition, gives a flavour of the life he briefly enjoyed – his best imperial primrose silk coat was laid across his body; his favourite zither, already an antique from the Tang dynasty by the time he came to use its jade tuning mechanism, was buried beside him.  Neither did Hongwu's edicts survive his death. His chosen teenage heir, his nephew, the Jianwen emperor, was quickly overthrown by another son, Zhu Di, who became the Yongle (or "perpetual happiness") emperor in 1402. One of the seismic changes introduced by Zhu Di was to develop his own fiefdom, Yan, as a secondary capital and to rename it Beijing. Many thousand of artisans and slaves were press-ganged to work on the construction of the palace complex that became the Forbidden City. Zhu Di dispatched fleets of ships on voyages of discovery and trade and created a multicultural imperial court, with artists absorbing influences from wider Asia and the Middle East, to create work of enduring beauty.  By the time of the accession of Zhu Di's grandson the Xuande "propagating virtue" emperor in 1426, much of the Forbidden City was complete (it has since been razed and rebuilt). The political heart of the imperial nation was not without its pleasures, as recorded in remarkable scrolls. One of these, six metres long, memorably unfurled for us at the Palace Museum of the Forbidden City, and which will be loaned to the London exhibition, depicts a kind of mini Olympiad. The emperor spectates at a version of football keepy-uppy among the beardless palace eunuchs, while other ink-on-silk panels depict archery competitions and see the emperor participating enthusiastically in a throw-the-arrow-in-the-jar challenge. The final panel shows the larger than life Xuande, with his wispy beard, borne away at the end of the day in a sedan chair, contemplating his idea of fun.  The ideal of the early Ming emperors was to be "complete in the arts of both peace and war" – until the sixth emperor failed disastrously in the latter and was captured by the Mongol armies in 1449 to bring a relatively harmonious era abruptly to a halt. Prior to that, in pursuit of "wen", the arts of peace, the emperors were all devotees of porcelain, and the new techniques introduced into the dozen imperial kilns produced ever more delicate pots and ever more brilliant glazes. It is a heart-in-mouth moment to watch curators blithely handling an imperial Ming vase (the trick, Harrison-Hall observed, before expertly manipulating a wonderful large blue-and-white wine jar decorated with ladies of the court at play, is just to hold it as you would any other object of similar heft – and never once give a thought to its priceless price tag).  The Yongle emperor, by necessity, and to propagandise his legitimacy, sought to spread his particular cultural revolution in different ways. When he appeared in public, a 2,000-strong choir sang and drums, cornets, cymbals and bells sounded (echoes of which we heard in the free-form harmonies of the 27th generation of imperial palace musicians, five of whom, trained in Ming notation, and playing authentic instruments, will travel to London to accompany the show).  In an effort to extend his influence still further, the emperor enlisted a comrade from his original march to power, the eunuch Zheng He, to make seven great voyages to the Middle East and East Africa, and to establish a "maritime silk route". Zheng He, a Muslim, was Marco Polo in reverse, taking the idea of China to the world in a fleet of treasure ships, some reputedly 140 metres long, and spreading the word of the great wealth and power of the Ming empire.  It is no surprise that Zheng He, virtually forgotten for centuries, has lately been reclaimed as a pioneering hero of an outward-looking and technologically advanced nation. The kinds of treasures he carried to foreign courts will once again be in transit this week, en route to the British Museum, generous loans from one gilded age of China's history that echo to the present.  Ming: 50 years that changed China (supported by BP) runs at the British Museum, London from 18 September to 5 January. Tim Adams travelled to China on a press trip supported by Shangri-La Hotels
Tim Adams reports on modern China's cultural leap forward and previews a historic show of treasures at the British Museum next month