Three people unaccounted for after a fire and explosion at a factory in Istanbul’s Tuzla district were declared dead, authorities announced on Friday.

A fire broke out at a paint factory in an industrial zone for paint manufacturers in Tuzla, located on city’s Asian side. Multiple explosions were heard following the fire as firefighters and paramedics rushed to the scene.

Nine people were reported injured earlier while a search was underway for three missing, after firefighters managed to curb the flames that sent a thick black cloud into the sky. Flames damaged the factory, as well as a small wooded patch near it and other businesses in the area. A firefighter was hospitalized for injuries sustained while trying to put out the fire.

The cause of the fire is unclear while an investigation is underway. Factory fires are quite common in Istanbul, which is one of the largest industrial hubs in Turkey’s west. Most are non-fatal but in February five foreign workers were killed when they were trapped in a small textile factory in Güngören district on the city’s European side.

Most fires stem from electric malfunctions and the textile and plastics industries are particularly vulnerable to blazes due to inflammable material used in production. Experts say inadequate maintenance of electricity systems and machinery in factories are usually the primary cause of the fires. A wave of factory fires in the past five years in Istanbul also stirred up conspiracy theories on social media about whether they were deliberately started by owners seeking insurance claims.