They advised residents to shelter in place and warned of risky driving conditions due to poor visibility.
The lava that has emerged over the last two weeks has destroyed at least 26 homes and 10 other structures.
The powerful, steam-driven blast was expected to spew large amounts of volcanic ash and smoke from Kilauea's crater on Hawaii's Big Island.
"The activity is such that they can occur at any time, separated by a number of hours", Hawaiian National Volcano Observatory Deputy Scientist-In-Charge Steve Brantley told reporters on a conference call.
Hawaii Gov. David Ige said the state is forming a joint task force that could handle mass evacuations of the Big Island's Puna district if lava from Kilauea volcano covers major roads and isolates the area.
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Lidington said the government was seeking legal opinion on both options, after reports suggested both could face legal hurdles. Mr Davis has reportedly told Mrs May that the customs partnership model she favours would be illegal under worldwide law.
Lava illuminates volcanic gases from the Kilauea volcano at fissure 13 on Hawaii's Big Island on May 16, 2018 in Pahoa, Hawaii.
"It's a real dynamic situation up there", she said of the summit. Mr Poland said the explosion probably only lasted a few minutes.
In a video, you can see ash plumes and flying debris clearly visible in the early morning skies. "I think it's going to be a series of explosions similar to the one that happened this morning, and that's based on what happened in 1924, which is really our only analog".
"I don't think there is a big one that's coming", said University of Hawaii vulcanologist Scott Rowland.
An animated GIF the USGS tweeted out shows how far the ash cloud might travel.
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The EU is also unimpressed by Trump's decision to place tariffs on European steel and aluminium as part of his "America first" agenda.
On Thursday, a 21st fissure also opened in Leilani Estates while other fissures reactivated with lava, the Hawaii Civil Defense said in an alert.
This is because Kilauea is a so-called shield volcano, which is typically broader in shape and has lava that is relatively fluid.
Even so, the county issued guidance to the community, noting that "The danger from this eruption is ash fallout", and added that residents need to protect themselves from the fallout.
The noxious gas, normally emitted at risky levels only from the volcano's Halemaumau Crater, was seeping at a greater rate from the fissures in Leilani Estates, a residential area of about four square miles in the Big Island's Puna district. But this is not Kilauea's first massive eruption.
But phreatic eruptions can still pose a deadly threat to anyone near the eruptive vent - and they are extremely hard to forecast, Poland said.
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