A firefighter was seriously injured battling an early morning blaze in Brooklyn that also left one person in critical condition and five others hurt, officials said.

Flames erupted at the home at 155 Avenue O near West 5th Street in Bensonhurst shortly after 4 a.m. Saturday, the FDNY said.

The fire, which started on the second floor, was brought under control in less than an hour.

The building has a storefront on the ground floor and two apartments above, according to several real estate sites.

More than 100 members of the FDNY responded to the two-alarm blaze, officials said. 

One unidentified “civilian” was taken to Staten Island University North in critical condition along with the firefighter, whose injuries were deemed “serious” but “non-life-threatening.”

Two other firefighters and three other civilians suffered minor injuries and declined medical attention, the officials said.

The cause of the fire is under investigation, the FDNY said.