Four Wilmington firefighters trying to save a family from a raging fire plummeted through a collapsing floor of the brick rowhouse early Saturday, a fall that killed two of them and critically burned the two others.

The residents - a woman, her five children, and a visiting child - had managed to escape through searing smoke out the back of the home. The woman and four of the children were treated for smoke inhalation after the 2:54 a.m. blaze.

Two additional firefighters, who were treated for less serious injuries - burns to their hands and forearms - and released from Christiana Hospital in Newark, Del., met later Saturday with fire officials in an effort to piece together the tragedy.

"This is a very tragic day for the Wilmington Fire Department, to lose two individuals, two of our brothers," Fire Chief Anthony Goode said.

He said the firefighters who were critically injured, a man and a woman, were being treated at the Crozer-Chester Medical Center burn unit in Upland. The female firefighter was airlifted to Crozer; the male firefighter was transported by Christiana Hospital's ambulance, Battalion Chief James Jobes said.

"All of our family is hurting significantly," Goode said. "The entire city is hurting significantly."

In a late-morning news briefing near the fire scene on the 1900 block of Lakeview Road, Goode identified those killed as Lt. Christopher Leach, 41, a 14-year department veteran, and firefighter Jerry Fickes, 51, who had been with the department 13 years.

"Both of them leave behind children and families," Goode said. "Please keep those children, those families, and all members of the Wilmington Fire Department in your prayers."

Goode said that as firefighters went inside the house, they were met with "significant heat and flames." He said the floor became "very soft and brittle" and began to collapse, crumbling below with the four firefighters.

Leach died at the scene, Jobes said. His colleagues carried him, draped with an American flag. Fickes was pronounced dead at Christiana Hospital.

An emotional Wilmington Mayor Dennis P. Williams said he had met with the families and children of the fallen firefighters.

"This is just a tragic situation," the mayor said at the news briefing.

A memorial and prayer service for the two fallen firefighters took place at 4 p.m. Saturday at the Salesianum School in Wilmington, where the high school posted on Facebook that Leach had graduated in 1994.

A resident of the burned rowhouse, Missy Napier, told the Wilmington News Journal that she, her five children, ages 10 to 17, and another child were sleeping when she awoke to find smoke.

"When it started, we started hollering, 'Get out of the house, get out of the house!' " After her children were rousted from sleep, they managed to escape out the back of the house.

"It was so hot; the smoke was burning your face," she said. "We ran out of the house with no clothes. My kids came out in basically nothing."

Goode said arriving firefighters were met with heavy flames at the back of the building.

"It's been rough, really rough," Napier said. "I had to go to hospital because I had an asthma attack."

Between sobs, she said that she and the children were OK.

"Emotionally we're struggling, but we're OK," she said.

The cause of the fire is not known and the cause of the two firefighters' deaths is being investigated, Jobes said. The Delaware Fire Marshal's Office is leading the investigation. The federal Bureau of Alcohol, Tobacco, Firearms and Explosives is also investigating.

"It's bad for all of us - bad for our city, bad for the Fire Department," Mayor Williams said. "What else can I say? My heart is heavy; I'm in so much pain right now."

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Staff writer Rebecca Heilweil contributed to this article.