By Caleb Davis
(Reuters) -Thirteen people were killed when a fire tore through a crowded nightclub in the Russian city of Kostroma in the early hours of Saturday, officials said.
The blaze broke out at about 2:30 a.m. in Polygon - an entertainment venue with a bar, restaurant and large dance floor - after a man shot a flare gun at the ceiling, the TASS news agency said.
"Very quickly the room began to fill with acrid smoke and the evacuation exits were difficult to see. There was pushing and panic," the agency reported, citing an eyewitness in Kostroma, which lies some 300 km (190 miles) northeast of Moscow.
In video footage posted on social media, people can be heard shouting while what appears to be a large cloud of thick smoke expands outwards from a fire on the ceiling.
Rescuers said 250 people were evacuated from the building.
"The flames were horrible, burning on several sides at once," said another witness.
Video shared by investigators showed firefighters spraying water on the smouldering, collapsed roof of the building. According to rescuers, the fire covered an area of 3,500 square metres and took about five hours to put out.
A 23-year-old man has been detained in connection with the incident, investigators said.
Prosecutors have also launched an investigation into the establishment itself, after finding that a number of the evacuation exits were blocked.
In 2009, 156 people were killed after a fire broke out at the Lame Horse nightclub in the city of Perm, sparking calls for tougher fire safety laws in a country where deadly blazes happen on a regular basis.
Local officials have declared Monday a day of mourning.