Although most of the lava flow is contained within the summit’s walls, residents have been warned about the danger of falling ash and placed on alert.
The US Geological Service (USGS), has stated that the situation could quickly change.
The alert level of the volcano has been elevated from an “advisory”, to a “warning”, the highest classification.
Officials from emergency services say that evacuation orders have not been issued yet and that affected areas are unlikely to be affected.
Mauna Loa, which is part of Hawaii Volcanoes National Park covers half the US state’s Big Island. The volcano rises at 13,679ft (4.169m), and covers more than 2,000 square miles (5.179 sq km).
It erupted at 23:30 GMT Sunday at Moku’aweoweo. Calderas are hollows formed beneath the summit during an eruption.
Following a series warnings that an eruption was possible, the incident occurred after a string earthquakes in this region, including more than a dozen tremors on Sunday.
A warning about ashfall, which can contaminate water supplies or kill vegetation, was in place for the immediate area overnight. However, it has since been lifted.
According to the USGS, “Based upon past events, the initial stages of a Mauna Loa volcano can be very dynamic and can result in lava flows moving quickly and changing their location.”
The eruption could move beyond the walls at the summit caldera and lava flows could “move swiftly downslope”, the report said.
According the USGS Mauna Loa erupted 33 times in total since 1843. The volcano that erupted in 1984 caused lava flows to be located within 5 miles of Hilo (the island’s most populous city).
The Big Island’s population is now around 200,000 and the civil defense agency in Hawaii has warned residents that they could face a “lava tragedy”.
“These lava flow rarely pose a risk to human life, but they can be very destructive to infrastructure,” stated Dr Jessica Johnson of the University of East Anglia. Johnson is a British volcano geophysicist who worked at the Hawaiian Volcano Observatory.
She said that the lava flow could be dangerous to Hilo, Kona and other major populations centres, as well as the possibility of breathing problems from volcanic gasses.
Mauna Loa, the world’s most active volcano, is located in Mauna Loa. There are also other volcanoes that are larger, but these are classified dormant. They haven’t erupted in a long time and are likely to not erupt again.
Mauna Loa shares Big Island space with Mauna Kea. Mauna Kea’s underwater base is nearly 20,000ft below ocean surface, making it the highest mountain in the entire world.