A fire ripped through a boardinghouse in South Korea early Friday, killing seven people and injuring 10 others, an official said.

The blaze occurred about 1:25 a.m. (1625 GMT) in Yongin, 30 miles south of the capital Seoul and it took firefighters 40 minutes to get it under control, fire official Yu Chang-seon said.

The seven who died are believed to have inhaled toxic gas, he said.

The fire also injured 10 others, three of whom were in serious condition. About 40 people were sleeping in the boardinghouse at the time.

Fire authorities were not sure what caused the blaze.