CHICAGO (WLS) — A fire that injured nine people in a North Side high-rise building Thursday afternoon was caused by unattended cooking, Chicago fire officials said Friday.

CFD called the fire accidental, and said it started in a fourth-floor unit. It spread through an open apartment door.

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One person was in critical condition, while eight others were taken to the hospital with serious injuries, after the blaze, CFD 2nd District Chief Robert Jurewicz said Thursday.

Dozens were rescued on the scene in the 5400-block of North Kenmore Avenue in Edgewater.

Part of the building is now uninhabitable. Some living on the upper floors had to be brought down by ladders, after the fire escapes filled with smoke.

The building was full of elderly residents.

Forty to 50-foot ladders were put up to rescue residents, some of whom were hanging out of the windows of the eight-story building.

Smoke was seen billowing out of the fourth floor, where the fire started in a rear apartment unit.

About 125 firefighters were on scene, working frantically both to fight the fire and to conduct the rescues, Jurewicz said.

It took around 75 minutes to put the fire out.

Officials said residents who have been displaced will eventually be allowed to return to their units, which should be undamaged as long as their doors remained closed.