A three-alarm fire raced through an apartment construction site in the North Capitol Hill neighborhood Wednesday, killing one person and forcing panicked construction workers to jump from the second and third floors to escape the flames.

The fire destroyed one building and damaged or destroyed dozens of vehicles, fire officials said. Six people were injured, including one who was in critical condition and one firefighter who suffered minor burns.

One person — believed to be a construction worker — remains unaccounted for, and firefighters searched in areas that were considered safe, fire Capt. Greg Pixley said at a news conference. Pixley said a body was found in the ruins of the building. Earlier, Pixley had said that two missing people were believed to be workers.

The fire broke out around noon in a five-story, 84-apartment building under construction at East 18th Avenue and Emerson Street, and the blaze sent flames shooting up to 200 feet high and a thick column of smoke billowing into a blue sky. Construction workers initially tried to put out the flames, but they were quickly overwhelmed.

More than 100 firefighters rushed to the scene, and they poured streams of water onto the flames from ladder trucks and from the ground. Fire hoses snaked across the surrounding streets as construction workers, residents and others gathered to watch the battle. At one point, crowds — with cellphones pointed at the inferno and mouths agape — had to shield themselves from the falling debris.

The heat from the flames was so intense that it sparked a fire at an adjacent building and melted nearby vehicles. Pixley said 30 vehicles and three fire engines were damaged or destroyed. Burning embers rained down on nearby buildings, sparking fires on the roofs of six buildings, and ash fluttered to the ground blocks away.

Hours after the flames were extinguished, the smoldering scene was still a “very dangerous and precarious environment” for firefighters, he said. It could take investigators a couple of weeks to determine the cause of the fire, Pixley said. Authorities have interviewed 100 witnesses so far, and he appealed to others to contact police or fire investigators with any other information.

He asked witnesses with any information to call 720-337-2800.

Some construction workers were injured when they jumped from the building and others were injured as they tried to catch them, Pixley said. About 50 workers were believed to be at the site when the fire broke out.

Mayor Hancock addresses media on Emerson st fire. One body has been found in ruins pic.twitter.com/4AVncjX4lQ — John Aguilar (@abuvthefold) March 7, 2018

Construction workers who were on the second floor of the unfinished building said they first noticed a smell like charcoal burning at a barbecue.

“It smelled a little bit like a barbecue, and then they told us to get out of the building,” said George Garcia.

Garcia and Junior Vega, who also was on the second floor, said they thought the fire started above them.

“It was quick, man,” Vega said.

Construction workers tried to douse the flames the best they could, Pixley said. He said the first call came in at 12:09 p.m., and it took firefighters 80 minutes to “reduce the volume of the fire.”

“If it wasn’t for the efforts of the construction workers and their efforts to look out for their own colleagues and do their best to reduce the amount of damage, it could have been a lot worse,” Pixley said.

Pixley said the fire burned so hot and so quickly because the building was under construction and wood was exposed.

“The building behind us had nothing to protect the wood,” Pixley said at a midafternoon news conference, as he gestured to the smoking ruins behind him.

In response to questions, Pixley said there is no reason to believe the building wasn’t following the city’s permit process. It was last inspected three days ago, and no issues were reported.

Emma Walker, manager of Urban Dogg at Washington Street and East 19th Avenue, said shortly after noon that she heard two loud explosions about 15 seconds apart and looked out the window to see black smoke.

A block closer to the fire, Kristen Cohen said she was in her home in the 1800 block of Clarkson Street when firetrucks with wailing sirens descended on her Uptown neighborhood.

“I went out on my porch, and it felt like I was next to the sun,” she said. “It was so hot.”

Staff members at the law offices of Rodger C. Daley were eating lunch in their building on East 19th when they heard a series of explosions. Attorney Carrie Vonachen said she heard up to 20 explosions, although two were louder than the rest.

“The heat was insane,” said Rachel Pisani, a paralegal at the firm.

Pixley said the explosions were probably the result of construction equipment — including compressed gas canisters and welding equipment — blowing up in the extreme heat. Car tires and gas tanks in vehicles could also have accounted for the explosions people heard.

The complex is being developed by Allante Properties in Greenwood Village. Darell Schmidt, managing partner at Allante, was out of the country at the time of the fire.

“We found out that our building just burned down, and I know absolutely nothing that happened other than it burned down,” Schmidt said. “I just found about 15 minutes ago.”

Denver’s office of emergency management has set up an evacuation center for anyone unable to return to their homes in the 1800 block of Emerson Street. The emergency shelter is at 3777 Lafayette St. Residents must bring identification and will be required to check in and complete paperwork. The shelter has capacity for 580 people.

People are encouraged to bring essential documents, cash and a flashlight. They also can bring books, magazines and quiet toys for kids. They are encouraged to bring food and supplies for infants. Arrangements will be made at the center to transfer pets to the Denver Animal Shelter.

People are not allowed to bring drugs, alcohol or weapons.