At least 51 people also were injured in the fire at the Grand Kartal hotel in Kartalkaya, in Bolu province's Koroglu mountains, some 300 kilometres east of Istanbul, said Interior Minister Ali Yerlikaya. The fire occurred near the start of a two-week winter break for schools, when hotels in the region are packed

"We are in deep pain. We have unfortunately lost 66 lives in the fire that broke out at this hotel," Yerlikaya told reporters after inspecting the site

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. Nine people have been detained as part of the investigation into the fire, Yerlikaya said. Earlier, Justice Minister Yilmaz Tunc said the hotel's owner was among the people detained for questioning in the probe

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