The world’s largest active volcano in Hawaii has exploded back to life after nearly 40 years, with a spectacular eruption in the summit caldera.

A warning was issued and two evacuation shelters opened after Mauna Loa began spewing lava and gases and triggered more than a dozen earthquakes in two hours.

The huge volcano takes up more than half of the Big Island in Hawaii and rises 4170 metres above the Pacific Ocean.

It’s the volcano’s first eruption since 1984 and ends its longest quiet period in recorded history.

Lava pours out of the summit crater of Mauna Loa. Photo: AAP

It began after more than a dozen earthquakes of more than 2.5 magnitude struck the region in the space of just two hours, according to the US Geological Service, with one measuring 4.2 in magnitude.

The night sky above Hawaii’s largest island glowed hellish red as rivers of molten lava poured from the summit about 11.30pm local time on Sunday.

The lava is contained within the summit and did not yet threaten Hawaiians living downslope, the USGS said.

A research camera on the north rim of the summit caldera of the Mauna Loa volcano captures the lava flow. Photo: AAP

The service warned residents on Monday that volcanic gases and fine ash might drift their way.

Mauna Loa is part of the chain of volcanoes that formed the islands of Hawaii.

It last erupted in March and April 1984, sending a flow of lava within 8.05 kilometres of Hilo, the island’s largest city.

Vents on the Northeast Rift Zone. Photo: AAP

Hawaii’s Emergency Management Agency said it had opened two shelters on the island as a precaution.

But the agency emphasised there were no signs that lava would threaten populated areas. It has not issued any evacuation orders.

About half of all recorded eruptions of Mauna Loa had been confined to the summit, the agency said.

The USGS’s volcanic activity service is monitoring the situation.

“At this time, lava flows are contained within the summit area and are not threatening downslope communities,” a notification said.

The crater of Mauna Loa when dormant. Photo: Getty

However, experience showed the early eruption stages could be very dynamic and the direction and speed of lava flows could change rapidly, the service advised.

The volcano alert level was upgraded from an “advisory” to a “warning.”

The notification added that the Hawaiian Volcano Observatory would conduct aerial reconnaissance as soon as possible to assess hazards and better describe the eruption.

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-with AAP