ATHENS, Greece (AP) — Three factory workers have been reported missing following a powerful explosion at a commercial dynamite factory in northern Greece, while one worker was hospitalized with light injuries, authorities said Monday.

The blast occurred outside the northern city of Grevena, 420 kilometers (260 miles) northwest of Athens.

Fire service rescuers were called to the site in a remote area 30 kilometers (19 miles) outside Grevena. Residents of the town heard the explosion, said regional governor Giorgos Kasapidis.

“This was a very large explosion that was detected dozens of kilometers away,” Kasapidis told state-run television.

“Explosives experts and rescue specialists are on the way to secure the site and make sure there are no secondary consequences from the initial explosion and to take other actions necessary while investigating the causes of the accident.”