Fountains of lava up to 60 metres high have been fired into the air from Hawaii's Mauna Loa, geologists have said, generating rivers of molten rock from the world's largest active volcano.

Four fissures have now opened up on the mammoth mountain, which burst into life on Sunday for the first time in almost 40 years.

Vast clouds of steam and smoke were billowing into the sky from the volcano, which makes up half of Hawaii's Big Island.

"Estimates of the tallest fountain heights are between 30-60 metres" but most are much smaller, the United States Geological Survey said in an update Monday.

"There is a visible gas plume from the erupting fissure fountains and lava flows, with the plume primarily being blown to the northwest."

Geologists say there is currently no risk to people and property below the eruption.

Mauna Loa has erupted 33 times since 1843

"The longest and largest lava flow is issuing from fissure three," the USGS said yesterday.

"This lava flow crossed the Mauna Loa Weather Observatory Road... and the flow front was located approximately 10 kilometers from Saddle Road (the main road at the foot of the northern flank)."

The lava fountain from the newest fissure was up to ten metres high, the agency said.

Everything is currently contained in the Northeast Rift Zone, the USGS said, but warned Mauna Loa is a dynamic volcano.

"Additional fissures could open along the Northeast Rift Zone below the current location, and lava flows can continue to travel downslope."

Pressure has been building at Mauna Loa for years, the USGS said, and the eruption, which lit up the night sky, could be seen 72km away, in the west coast town of Kona.

'Long Mountain'

While lava is not presently a risk to populations, scientists have said winds could carry volcanic gas and fine ash downslope, as well as Pele's Hair - fine strands of volcanic glass formed when lava skeins cool quickly in the air.

Named after Pele, the Hawaiian goddess of volcanoes, the strands can be very sharp and pose potential danger to skin and eyes.

Authorities in Hawaii have not issued any evacuation orders, although the summit area and several roads in the region were closed, and two shelters have been opened as a precaution.

The largest volcano on Earth by volume, Mauna Loa, whose name means "Long Mountain," is larger than the rest of the Hawaiian islands combined.

The volcano's submarine flanks stretch for miles to an ocean floor that is in turn depressed by Mauna Loa's great mass -- making its summit some 17km above its base, according to the USGS.

Mauna Loa is one of several volcanoes on the island

One of six active volcanoes on the Hawaiian islands, Mauna Loa has erupted 33 times since 1843.

Its most recent eruption, in 1984, lasted 22 days and produced lava flows reached to within about four miles of Hilo.

Kilauea, a volcano on the southeastern flank of Mauna Loa, erupted almost continuously between 1983 and 2019, and a minor eruption there has been ongoing for months.