In an event that had been anticipated for days, molten lava from Kilauea Volcano burst forth into Lower Puna on Thursday afternoon, prompting the evacuation of more than 1,800 residents.

The vent opened up with steam and lava emissions shortly after 4 p.m. off Mohala Street, officials said. Splattering molten rock shot into the air, and flowing lava spread onto the street and into the neighboring open forest.

The Hawaii County Civil Defense Agency immediately closed roads around the Leilani Estates subdivision and began a mandatory evacuation of residents there and in the neighboring Lanipuna Gardens subdivision.

Eyewitness accounts suggested that some homes appeared to be threatened.

Lower Puna resident Ikaika Marzo said he saw lava fountains shooting up to 150 feet in the air, with molten lava spreading out in an area 200 yards wide behind a house on Mohala Street.

“It sounds like a jet engine. It’s going hard,” he said.

Hawaii Volcano Observatory scientists said late Thursday that a 492-foot-long fissure erupted with lava bubble bursts for about two hours. The flowing lava traveled a few yards from the fissure and stopped, the scientists said.

The eruption is not over, as there continues to be volcanic activity in the area, observatory scientists said. “At this point it is wait and see what happens next,” said Janet Babb, Hawaii Volcano Observatory geologist.

Marzo, who runs a concession in Kalapana, was urging followers on social media to come to Leilani Estates to help people evacuate.

“There are a lot of elderly people who need help to get their stuff out,” Marzo said.

But Civil Defense officials were telling people to avoid traveling to the evacuation area “for everyone’s safety.” Only residents would be granted access, they said.

Road closures were in effect at Highway 130 and Leilani Boulevard, Highway 132 and Pohoiki Road, and Highway 137 and Pohoiki Road.

Shelters were opened at the Pahoa Regional Community Center near the new Pahoa Regional Park and the Keaau Community Center.

Residents were asked to bring an emergency evacuation supply kit, including necessary medicine, food and other items. Others were asked to stay tuned to local news and radio for updates.

Leilani Estates resident David Moore, who was in Honolulu and flying back to the Big Island on Thursday night, said his wife, Christina Moore, was at the Pahoa shelter.

A friend brought news of the eruption to their Malama Street home Thursday afternoon.

“She didn’t even know about the evacuation,” he said.

Moore said his wife was so flustered that she went to the shelter with the friend, grabbing the registration to their Toyota Camry but not the car or any clothes.

In Honolulu, Gov. David Ige activated the Hawaii National Guard to provide support to county emergency personnel to help with evacuations and security.

A Hawaii National Guard spokesman said soldiers will be brought in today to assist local officials, although he didn’t know how many.

“I am in contact with Mayor (Harry) Kim, and the state is actively supporting the county’s emergency response efforts,” Ige said in a statement. “I urge residents in Leilani Estates and the surrounding areas to follow instructions from the County of Hawaii’s Civil Defense Agency. Please be alert and prepare now to keep your family safe.”

Both Ige and Hawaii County Acting Mayor Wil Okabe signed emergency proclamations expected to lead to additional funding for disaster relief and emergency management.

Hawaii Volcano Observatory geophysicist Asta Miklius said white-hot vapor and blue fumes began emerging from cracks in the Leilani Estates subdivision Thursday afternoon, and lava was confirmed to have surfaced shortly before 5 p.m.

Observatory teams were deployed to the scene on the ground and in the air, while staff continued to monitor streams of data, she said.

Miklius said that while the Leilani Estates subdivision appears to be at greatest risk, areas downslope of the erupting vent are also in danger. The opening phases of fissure eruptions are unpredictable, she said, adding that additional vents and new lava outbreaks could occur.

After the outbreak, the nearby 38-megawatt Puna Geothermal Venture power plant began executing its emergency plan and started shutting down operations, officials said.

A spokeswoman for Hawaii Electric Light Co. said that despite the shutdown, the utility has enough power to handle the island’s needs without resorting to rolling blackouts or other emergency measures.

Kilauea has been showing signs of a new eruption for days, with the migration of earthquakes and magma into the Lower Puna area.

On Thursday Puna residents were on edge following a magnitude-5.0 earthquake and large pinkish plume that rose above Puu Oo vent, which was seen for miles.

Earlier in the day, the lava lake at the Halemaumau summit dropped in level by more than 100 feet. The last time that happened was in March 2011, when the Kamoamoa fissure opened to a five-day eruption, said Babb, the geologist.

Also on Thursday the sluggish and remote 61g eruption was declared dead, following an aerial survey that could not find any signs of volcanic activity, Babb said. The 61g flow started in May 2016 and eventually created a spectacle when it poured into the the ocean.

“It’s an indication that things are changing on Kilauea,” she said.

Miklius said the recent migration of earthquakes eastward along the east rift zone recently stopped at just about Leilani Estates, a possible sign that lava might emerge in that area.

At Hawai‘i Volcanoes National Park, officials Thursday ​​closed Naulu Trail, parts of Napau Trail and adjacent wilderness areas in the east rift zone for public safety.

Some 31,660 acres, or less than 10 percent of the 333,308-acre park, are now closed, a park spokeswoman said.

Staff writers Gordon Pang and Dan Nakaso contributed to this story.