At least 22 firefighters were hurt battling a four-alarm blaze that tore through a duplex on Staten Island on Friday, the FDNY said.

Three firefighters with serious injuries were taken to Staten Island University Hospital, where they remain in stable, but critical condition, FDNY Commissioner Laura Kavanagh said at a Friday evening press conference from the hospital. The other 19 suffered minor injuries, she said.

No civilians were believed to be injured, according to the commissioner.

"They're alert, they're talking, they're cracking jokes, which we're very grateful for," Kavanagh said of the three firefighters who sustained serious injuries.

At another press conference just before 4:30 p.m. Friday at the scene of the fire, FDNY Chief Brian Gorman — the acting Staten Island borough commander — said the FDNY received a call reporting a fire at 88 Shotwell Ave., near Waring Avenue in Arden Heights, just before 1:30 p.m. Upon arrival, firefighters discovered a "heavy fire" in the rear of the building, Gorman said.

The fire spread to an adjacent home at 84 Shotwell Ave. as well, Gorman said.

FDNY Chief of Department John Hodgens said at the later press conference that one of the firefighters who was seriously injured leapt out a second-floor balcony onto the driveway. Another firefighter, a lieutenant, "transmitted a mayday signal" from the second floor of one of the homes and was rescued by his fellow firefighters, the chief added.

"I cannot emphasize enough that this was a very close call for the FDNY. We could have lost three members today," Kavanagh said. "But it was thanks to the brave work of our members, including those who went in and saved their fellow firefighters, rescued the trapped members" that the injured firefighters are still alive.

The firefighters had entered the homes to search for occupants, Hodgens said. Strong winds blew the flames into the home, trapping the firefighters, he explained.

Another firefighter, a nozzelman, was hit in the head by falling debris and inhaled smoke, Hodgens added.

Part of the rear extension of 84 Shotwell Ave. suffered a "major collapse," according to Gorman.

The cause of the fire is still under investigation, Hodgens said, but that the FDNY believes it started between two smaller structures attached to the duplex where the fire spread.

As of around 2:45 p.m., firefighters had brought the blaze under control, according to the FDNY. Over 200 firefighters and paramedics responded.

The city's Department of Buildings said inspectors visited the homes Friday afternoon and determined the rear extension to 88 Shotwell Ave. was constructed without the proper permits. The owner of 88 Shotweel Ave. was issued a violation by inspectors for "illegal unpermitted work," a DOB spokesperson said.

The extension completely collapsed during the fire, according to DOB officials.