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Six children were found dead after an early morning house fire in Baltimore, officials said Thursday, as the children’s mother and three other siblings were taken to a hospital for treatment.

Firefighters had pulled five bodies from the destroyed home Thursday, but the age and gender of the victims had not yet been determined, fire officials said. A sixth child, a 9-month-old boy, was recovered later Thursday afternoon.

"To know that so many children are not going to be with us is painful," Baltimore Mayor Catherine Pugh said at a press conference Thursday afternoon.

Authorities arrived to battle the blaze at the three-story home in Baltimore, Maryland, at 12:30 a.m. on Thursday, Baltimore Fire Chief Roman Clark said.

The third floor of the building had collapsed onto the second floor, he said.

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Baltimore City firefighters remain on the scene early on Jan. 12 after a fire on Springwood Avenue in northeast Baltimore. Jerry Jackson / Baltimore Sun via AP

"This collapse was horrendous," Clark said. Three of the victims were recovered from the second floor and two were recovered from the first floor, he said. The infant was found on the first floor in a crib.

A woman and three children had escaped the burning home by the time firefighters arrived and were sent to local hospitals for treatment, Clark said. The rescued children were an 8-year-old girl, 5-year-old boy and 4-year-old boy, Clark said at a press conference Thursday afternoon. The woman and two of the children were in critical condition, but the 8-year-old girl was expected to be released from the hospital later Thursday, Frank said.

The girl had managed to rescue her other two siblings, pulling them from the burning home, he said.

Six other children, ranging in age from 9 months to 11 years old, had been unaccounted for in the blaze, Frank said at the press conference. All were members of the same family.

The missing children had included a 9-month-old male, 2-year-old male, two 3-year-old female twins, a 10-year-old female, and an 11-year-old female, Clark said.

"They couldn't put the fire out, it was so strong,” Paul Keve, a witness who was going to the store at the time of the fire, told NBC News.

"People where there crying. It was a total mess out there last night," Keve said.

Debris from an early morning house fire is seen past fire officials in Baltimore, Thursday, Jan. 12. Patrick Semansky / AP

Officials said the children's father was at work at the time of the incident and said he had recently changed the battery in the home's smoke alarm. The cause of the blaze was still under investigation.

The family was not identified by name by authorities, but Pugh said the mother was an aide to Rep. Elijah Cummings, D-Md.

Cummings released a statement identifying the mother as Katie Malone.

“I am asking that our entire community pray for my staff member, Katie Malone, and her young family," he said in the statement. Malone was a special assistant to Cummings, Cummings said, and worked in the areas of immigration, postal services and the military.

"My staff is a family and this unimaginable tragedy is shocking and to us all," Cummings said.