Four workers were injured, two seriously, in an explosion occurred on Tuesday at a metal processing factory in the western Japanese prefecture of Osaka, local officials said.

The accident happened at round 11 a.m. local time at the plant in Sakai City of the prefecture, and local rescue teams carried the four men to hospitals according to the spokesperson at the city's fire bureau.

The spokesperson told Xinhua that the most seriously injured of the four is a 35-year-old worker who was badly burned after the blast, adding that he is in a life-threatening condition after he was rescued from the blast site, and another 54-year-old man is also treated in a specialized burn unit of the hospital.

The accident happened at a melting furnace in the plant, and local police and the fire department are jointly investigating details of the explosion, the spokesperson said.

The factory belongs to Nippon Shindo Company, which is mainly engaged in the manufacture and sale of copper products.