Two people rescued from the central Australia floods were found severely dehydrated after trekking 58km across the outback.  The 30-year-old man and 27-year-old woman were part of a group of six who went missing when they attempted a Christmas Day trip from the Kiwirrkurra Community in Western Australia's Gibson Desert.  Acting Superintendent Brendan Muldoon said it was extraordinary that they had managed to walk so far across the desert in two days.  "They walked a small access drive off the main road which made our efforts a lot more difficult in that they continued to movem which hampered our rescue efforts," he said.  A helicopter rescued four of the six on Tuesday afternoon, after they failed to make the 180km trip to Kintore in the Northern Territory.  The final two were spotted on foot almost 60km away on Wednesday and have been taken to Kintore medical centre to be treated for dehydration.  A pair of tourists are also lucky to be alive after their rented car was swept off a causeway near Alice Springs.  The man and woman, from Hong Kong and Taiwan, managed to escape from the vehicle as it was washed down the Hugh River on Tuesday.  Supt Muldoon said it was remarkable they weren't killed and commended the "very courageous" officers and bystander who risked their own lives to save them.  "They've put themselves in harm's way, no doubt about that, but they've done it in the belief that if they hadn't done so those people would have most likely died," he said.  "It was an extremely dangerous road they have tried to cross in those floodwaters."  The man was found clinging to a tree in the river and the woman was discovered unconscious on the shore.  Police initially thought there were three people inside the vehicle but have since confirmed that there were only two.  About 50 people will spend at least another night in an emergency shelter after their houses were swamped by the floodwaters.  On Wednesday night the Bureau of Meteorology issued a severe thunderstorm warning for parts of central Australia, saying it may lead to flash flooding around Yuendumu, Wulungurru, Tennant Creek, Ali Curung, Ti Tree and Ampilatwatja.
Two people who set off for help after being caught in flood waters in the Top End remain missing, but their four companions have been found safe.