Mauna Loa: World's largest active volcano erupts in Hawaii

The world's largest active volcano, Hawaii's Mauna Loa, is erupting for the first time in almost 40 years.

"Lava flows are contained within the summit area and are not threatening downslope communities," officials said.

But the notification from the US Geological Service (USGS) warned the situation could change rapidly.

An ashfall advisory is in effect for Hawaii's Big Island and the surrounding waters, and residents have been told to remain vigilant.

The volcano's alert level has been upgraded from an "advisory" to a "warning", its highest classification.

Mauna Loa last erupted in March and April of 1984, sending lava flows within 5 miles (8km) of the city of Hilo.

The latest eruption began on Sunday night at Moku'āweoweo, the volcano's summit caldera. Calderas are hollows that form beneath the summit at the end of an eruption.

It followed a series of warnings that an eruption was possible after a spate of recent earthquakes in the region, including over a dozen tremors measured at more than 2.5 magnitude on Sunday.

"Based on past events, the early stages of a Mauna Loa eruption can be very dynamic and the location and advance of lava flows can change rapidly," the USGS said.

If the eruption migrates beyond the walls of the summit caldera, lava flows could "move rapidly downslope", it added.