ANKARA, Turkey — A fire raged through a 12-story hotel at a popular ski resort in northwestern Turkey early Tuesday during a school holiday, killing at least 76 people — at least two of them when they jumped from the building to escape the flames, officials said.

At least 51 people were also injured in the fire at the Grand Kartal hotel in Kartalkaya, in Bolu province’s Koroglu mountains, some 185 miles east of Istanbul, Interior Minister Ali Yerlikaya said.

The fire occurred near the start of a two-week winter break for schools, when hotels in the region are packed.

“Our hearts are broken. We are in mourning,” Yerlikaya told reporters outside the hotel. ”But you should know that whoever is responsible for causing this pain will not escape justice.”

Atakan Yelkovan, a hotel guest staying on the third floor, told the IHA news agency there was chaos on the upper floors as other guests tried to escape the fire, including by trying to climb down from their rooms using sheets and blankets.

“People on the upper floors were screaming. They hung down sheets. ... Some tried to jump,” Yelkovan said.

Health Minister Kemal Memisoglu said at least one of the injured was in serious condition, while 17 other people were treated and released.

The hotel had 238 registered guests, Yerlikaya said. The fire was reported at 3:27 a.m. and the fire department began to respond at 4:15 a.m., he told reporters.

The government appointed six prosecutors to lead an investigation into the blaze, which is believed to have started in the hotel’s restaurant section. Justice Minister Yilmaz Tunc said four people, including the hotel’s owner, were detained for questioning as part of the investigation.

At least two of the victims died when they jumped from the building in panic, Gov. Abdulaziz Aydin told the state-run Anadolu Agency earlier. Those killed included Nedim Turkmen, a columnist for Sozcu newspaper, his wife and two children, the newspaper announced.

Turkish President Recep Tayyip Erdogan announced a day of national mourning to be observed today. All flags at government buildings and Turkish diplomatic mission abroad would be lowered to half-staff, he said.

Necmi Kepcetutan, a ski instructor at the hotel, said he was asleep when the fire erupted and he rushed out of the building. He told NTV television that he then helped some 20 guests out of the hotel.

The hotel was engulfed in smoke, making it difficult for guests to locate the fire escape, he said.

“I cannot reach some of my students. I hope they are OK,” the ski instructor told the station.

Television images showed the roof and top floors of the hotel on fire. Witnesses and reports suggested that the hotel’s fire detection system failed to operate.

“My wife smelled the burning. The alarm did not go off,” said Yelkovan, the guest interviewed by IHA. “We tried to go upstairs but couldn’t, there were flames. We went downstairs.”