A fire at a ski resort hotel in Turkey's Bolu mountains killed 76 people and injured dozens on Tuesday, forcing panicked guests to jump out of windows in the middle of the night.

"It was like the apocalypse. The flames engulfed the hotel immediately, like in half an hour," said Mevlut Ozer, who witnessed the incident at the Kartalkaya ski resort in northwest Turkey.

The fire began around 3:30 a.m. (0030 GMT) on the restaurant floor of the 12-storey Grand Kartal Hotel, authorities said.

Several fire engines and ambulances later surrounded the charred, wood-fronted building, where white bed sheets tied together dangled from at least three upper-floor windows, showing how people tried to flee.

President Tayyip Erdogan declared Wednesday a day of national mourning after the incident.

"People all started to jump with panic. One friend jumped from the 11th floor - may God have mercy on him," said Omer Sakrak, another witness and employee of a neighbouring hotel.

"They tried to climb down using bedsheets. The bedsheets ripped as one friend tried ... and he unfortunately fell on his head," he told Reuters. "One father was yelling about his one year-old child: 'I will throw my child or he will burn'."

Hotel guests told TV broadcasters they fled through smoke-filled corridors and heard no alarms.

Interior Minister Ali Yerlikaya said there had been 238 guests staying at the hotel, situated at the base of several ski slopes, which smouldered until the afternoon.

"Our pain is impossible to describe," he said, speaking from the resort and offering condolences. Yerlikaya said the fire was out and that search efforts at the hotel had finished.

Authorities are conducting DNA tests to identify some of the bodies recovered from the scene of the fire, he added.

An investigation was underway into the fire, which happened during school holidays when many families from nearby Istanbul and Ankara head to the Bolu mountains to ski.

Police detained nine people as part of the investigation, Yerlikaya said, adding that prosecutors will shed light on the cause of the fire and people responsible will be brought to justice.