An explosion at an unlicensed fireworks factory in Istanbul killed 17 people and injured 68 others Thursday, an official said. "The blast was caused by the fireworks," Gov. Muammer Guler said. Four of the injured were in critical condition, he said. A statement by Istanbul Health Directorate said at least eight people were seriously injured. Guler said there had been a small fire on the fourth floor of the building before the explosion occurred. A blast minutes killed eight people who were watching the fire, he said. Earlier, a witness who identified himself as Ali told private CNN-Turk television that he heard two explosions, five minutes apart, while working at a nearby factory. "White smoke was rising into the sky from the factory as we came to the front of the building. People were running around. I helped carry out six injured people," he said. Businesses in the five-story building included textile makers and an unlicensed fireworks manufacturer, according to local media. Nearby buildings also were damaged. Part of the factory building in the Davutpasa district of Istanbul collapsed following the explosion. Police sealed off the area as rescue workers tried to pull out six bodies trapped under the debris. Earlier, television footage showed at least two men lying in the street. Another man with blood on his face walked nearby. Rubble lay strewn around the shattered building, and falling debris had smashed several vehicles.