A factory producing rubber footwear, north of the capital of Manila, was razed by a fire on Wednesday, and authorities feared that dozens of workers reported missing could have perished in the fire. Fire officials, cited by a local news outlet, said at least 31 people perished in the blaze.

At least three bodies were recovered from the factory in the city of Valenzuela, and fire officials said they had not found any survivors after it was contained, according to Mayor Rex Gatchalian, the Associated Press reported. Gatchalian said the fire was apparently caused by sparks from welding works at the building’s main entrance.

Relatives of the factory’s employees reported 62 people missing, but Gatchalian said only seven of them were reported to have survived. He added that there could be others who had escaped and had not yet been found, but said that nobody had yet come forward to confirm that.

District Fire Marshall Wilberto Rico Neil Kwan Tiu said he saw “numerous bodies,” many burnt beyond recognition, on the building’s second floor. Escaping workers told local media that many of those inside were unable to escape because of the heavy smoke blocking the building’s entrance, according to Al Jazeera.

It is unknown if the factory had an emergency fire exit.