Mauna Loa: World's largest active volcano erupts for first time in 38 years

Watch: World's largest active volcano, Hawaii's Mauna Loa erupts

Waves of orange lava and smoky ash belched from Hawaii's Mauna Loa volcano on Monday in its first eruption in 38 years.

The eruption of the world's largest active volcano was not immediately endangering towns, but officials told people on Hawaii's Big Island to be prepared for worst-case scenarios.

The US Geological Survey warned that eruptions "can be very dynamic, and the location and advance of lava flows can change rapidly".

Officials told residents to be ready to evacuate if lava flows start heading towards populated areas. Hawaii County Civil Defence announced it had opened shelters because it had reports of people already evacuating on their own initiative.

Volcano - BRUCE OMORI/PARADISE HELICOPTERS/EPA-EFE/Shutterstock
Volcano - BRUCE OMORI/PARADISE HELICOPTERS/EPA-EFE/Shutterstock

Scientists had been on alert because of a recent spike in earthquakes at the summit of the volcano, which last erupted in 1984.

Ken Hon, the lead scientist at the Hawaiian Volcano Observatory, said the eruption began late on Sunday following a series of fairly large earthquakes.

Mauna Loa - US Geological Survey/AFP/Getty Images
Mauna Loa - US Geological Survey/AFP/Getty Images

The areas where lava is emerging - near volcano's summit crater and vents along the its north-east flank - are both far from homes and communities.

Officials urged the public to stay away due to the dangers posed by the lava, which is shooting 100 to 200 feet into the air out of three separate fissures roughly one to two miles long.

Volcanic gases wafting out of the vents, primarily sulfur dioxide, are also harmful.

Mauna Loa - US Geological Survey/AFP/Getty Images
Mauna Loa - US Geological Survey/AFP/Getty Images

Air quality on Big Island is currently good, but officials are monitoring it carefully, said Libby Char, the director of the state Department of Health.

Mr Hon added that air quality could deteriorate throughout the eruption, which scientists expect will last around one or two weeks if the volcano follows historical patterns.

Bobby Camara, a lifelong resident of Big Island, said he had seen three Mauna Loa eruptions in his lifetime and stressed the need for vigilance.

"I think everybody should be a little bit concerned," he said. "We don't know where the flow is going, we don't know how long it's going to last."

Lava pours out of the summit crater of Mauna Loa on Monday, as seen from Gilbert Kahele Recreation Area - AP
Lava pours out of the summit crater of Mauna Loa on Monday, as seen from Gilbert Kahele Recreation Area - AP

Gunner Mench, who owns an art gallery in Kamuela, said he awoke shortly after midnight and saw an alert on his phone about the eruption.

Mr Mench and his wife, Ellie, ventured out to film the eerie red glow cast over the island, watching as lava spilled down the volcano's side.

"You could see it spurting up into the air, over the edge of this depression," Mr Mench said. "Right now it's just entertainment, but the concern is it could reach populated areas."

Seeing Mauna Loa erupt is a new experience for many residents of Big Island, where the population has more than doubled from 92,000 in 1980.

More than a third of the island's residents live either in the city of Kailua-Kona to the west of the volcano, and in Hilo to the east.

Mauna Loa - Marco Garcia/AP
Mauna Loa - Marco Garcia/AP

Officials are most worried about several residential areas around 30 miles to the volcano's south that are home to about 5,000 people.

The US Geological Survey said the eruption had migrated to a rift zone on the volcano's north-east flank. Rift zones are where the mountain rock is cracked and relatively weak, making it easier for magma to emerge.

Lava could move toward the county seat of Hilo, but that could take about a week, Mr Hon said.

Scientists hope the flow will parallel the 1984 eruption, where the lava was more viscous and slowed down.