CHARLESTON, W.Va. (AP) _ Unidentified fumes were reported near two chemical plants Thursday, and six people were overcome after breathing them, authorities said.

The source or composition of the fumes could not be determined, although city officials were treating it as a chemical leak and contacted the two companies, Union Carbide Corp., and FMC Corp., said Kent Carper, the city's public safety director.

''No one has indicated to us that they are responsible for any type of chemical release,'' Carper said, adding that the source may never be known.

Officials of both chemical companies said they were investigating the fumes and did not know whether they were coming from their plants, which are within a mile of each other.

The incident occurred about 1:40 p.m. near the Patrick Street Bridge, which is close to the two plants, when a smell ''like fingernail-polish remover, kind of an acetone smell,'' was reported, said Fire Capt. Mark Wolford.

Crews were dispatched to the scene after receiving several calls from people at a car dealership who reported feeling ill, said Fire Capt. Raymond Debolt. The odor dissipated within 30 minutes, he said.

Those overcome by the fumes complained of severe headaches and eye, nose and throat irritation, he said.

Wolford said those overcome by the fumes complained of severe headaches and eye, nose and throat irritation.

Two of those who were overcome, Richard P. Johnson, 47, and Kevin McNeely, 19, were treated at Charleston Area Medical Center and released, a spokesman said.

Union Carbide spokesman Dick Henderson said employees immediately began checking the company's nearby South Charleston plant but could not find the source of the fumes.

''We've been checking all the production units,'' he said. ''At this point we have been unable to pinpoint any source of leakage.''

Sam Harris, administrative assistant to the plant manager at FMC, also said crews were investigating. He described the odor as resembling ''ether or paint thinner.''