Low lava fountains from the Kilauea volcano were erupting from a nearly continuous 3km-long portion of the series of fissures that have opened up in the ground, scientists said on Thursday.

The fountains were feeding channelised lava flows down to the coast. The eastern-most channel split on Wednesday, creating three ocean entries.

Since the eruption began on May 3, Hawaii County has ordered about 2000 people to evacuate from Leilani Estates and surrounding neighbourhoods.

Hawaii officials have said they may need to evacuate a thousand more people if lava crosses key highways and isolates communities in the mostly rural part of the island where the Kilauea volcano is erupting.

A blocked highway would cut people off from the only route to grocery stores, schools and hospitals.

The US Marine Corps said on Thursday that it had sent two CH-53E Super Stallion helicopters from a base near Honolulu to help if more evacuations become necessary. Each helicopter can carry 50 passengers.

The volcano has opened more than 20 vents in the ground that have released lava, sulphur dioxide and steam.

Lava has destroyed 50 buildings, including about two dozen homes. One person was seriously injured after being hit by a flying piece of lava.

There continues to be intermittent explosions at the summit that have been sending plumes of ash into the sky.

On Wednesday, the volcano belched a plume that reached about 2130 metres high, scientists said. Right before the explosion, there was a 3.9 magnitude earthquake at the summit.

"We are kind of in this steady state," said Wendy Stovall, a scientist at the US Geographical Survey.

There's no indication about whether lava volume will increase or decrease, she said. The continued explosions are expected to "last a little while longer."

Australian Associated Press