A LARGE explosion at the heart of Hawaii’s Kilauea volcano could plunge the island into further turmoil.

The US Geological Survey has warned more violent eruptions at the crater could being in mid-May, with potentially devastating effects.

Rocks weighing several tonnes could fly as far as 1km, according to the survey, with pebble-sized projectiles landing even further.

Houses up to 32km away could also end up covered in volcanic ash.

The risk will rise as lava drains from the summit crater down the flank of the volcano, and explosions could occur if the lava drops below the groundwater level.

“This is the first of perhaps more events like that to come,” Tina Neal, the scientist in charge of the USGS Hawaiian Volcano Observatory said of Wednesday’s blast, which shot projectiles from the crater.

The steam-driven explosions would be triggered by water running into the crater’s falling lava lake should it drop below the level of groundwater.

Hawaii County Civil Defense said all 1,900 residents of the Leilani Estates and Laipuna Garden areas, around about 40km east of the crater, had been evacuated. Lava oozing from two new fissures in the area had paused but sulphur dioxide gas was still a hazard.

Evacuee David Nail was anxious to learn if his house had been destroyed. He was asleep on the couch when a fissure opened up 610m away, spewing out lava and gas.

“It sounded like 10 or 20 jet engines,” said Mr Nail.

The 57-year-old said he had seen drone footage showing lava flowing up his driveway, causing two propane tanks to explode.

He tried to reach his house on Tuesday, but he and his neighbours were blocked by a 20-foot tall wall of lava.

“All we could do was sit there and cry,” he said.

It has destroyed 36 structures since it began releasing lava from fissures that opened in a Big Island neighborhood about 40.2 kilometres east of the summit crater.

There are now 15 of the vents spread through Leilani Estates and neighboring Lanipuna Gardens.

In the weeks ahead, the volcano could eject blocks up to 1.8 metres in diameter a little less than 1.6 kilometres away, the USGS said.

The receding lava lake resembles conditions seen before a major summit eruption in 1924, said Tina Neal, scientist-in-charge at the USGS Hawaiian Volcanoes Observatory.

That explosion killed one person and sent rocks, ash and dust into the air for 17 days.

This event could occur again when the lava lake drops so low that groundwater is able to flow into the conduit that feeds magma to the summit crater. The magma would heat the water, sending steam into the air that would push any accumulated rocks out in an explosion.

Don Swanson, a geologist with the Hawaiian Volcano Observatory, said the magma is likely to drop below the water table around the middle of the month. Scientists don’t know how long after that it an explosion could occur. “We suspect it’s a rapid process. We really don’t know for certain,” he told reporters on a conference call.

No one lives in the immediate area of the summit crater. The Hawaii Volcanoes National Park, which includes the crater and surrounding region, announced Wednesday that it will shut down Friday in anticipation of the possible explosive event.

“It seems pretty safe to me right now but they’d know best,” said Cindy Woodd, who was visiting from British Columbia, Canada. “We don’t know what’s going on underground. Life and safety is what’s most important.”

Kilauea, Hawaii’s most active volcano, erupted last week and a powerful earthquake shook the crater the next day.

The event was marked with lava shooting more than 90 metres into the air. Fourteen fissures have opened since then, with lava covering more than 42 hectares of land.

Kilauea has been in a state of nearly constant eruption for 35 years. It predominantly blows off basaltic lava in effusive eruptions that flow into the ocean but occasionally experiences more explosive events.