BEIJING, July 29 (Xinhua) -- China's work safety authorities will investigate and crack down on manufacturers operating illegally in the coming three months, the Work Safety Committee Office under the State Council, China's Cabinet, said Wednesday.

Accidents in manufacturing plants have dropped this year, but illegal operations still pose a grave threat to workplace safety, accounting for about 55 percent of the accidents above "relatively major" level, said a statement from the office.

An accident above "relatively major" level referred to a case in which three or more deaths are involved, ten or more are seriously injured or an economic loss above 10 million yuan (1.48 million U.S. dollars) is caused.

The crackdown beginning from Aug. 1 will focus sectors including mines, transportation, construction sites, manufacturers of dangerous chemicals, fireworks plants and smelting sector, said the statement.

Illegal operations mainly refer to manufacturers that run without permits or run with insufficient or overdue permits and against safety production laws and codes.