At least 6 people were killed and 27 others were reported missing in a massive explosion taking place at a plant in South Korea's Icheon city on Monday, a police officer of Icheon told Xinhua.

"We have found six bodies and are making efforts to put out the fire on the spot," said Yu Jeon-hwan, an officer of the Incheon Police Station.

"The heavy and toxic smoke made the rescue work very difficult," he said, adding those remaining missing might have little possibility to survive.

The identities of the victims are unknown as local police and firemen are focusing on rescue works, Yu said.

"We don't know whether there are foreign labors among the victims," he said.

According to local police, the accident occurred at 10:49 a.m.( 0149 GMT Monday) at the basement of a logistic hub in Icheon city.

Local police said there were 54 people working at the basement when the explosion took place.

As of 2:00 p.m.(0500 GMT), only 21 people escaped or were rescued from the spot of accident, the police said.

Among the rescued people, more than 10 have been sent to hospitals nearby and some of them are in critical conditions, local report said.