The lingering corrosive mist left over from a concentrated hydrochloric acid spill in Songjiang district is expected to clear up Thursday, local media reported.

Although acid levels in the air had fallen by 90 percent as of noon Wednesday, they remained above environmental standards, said Shen Jing, a press officer for the Songjiang District Environmental Protection Bureau.

The spill occurred around 6:15 pm Tuesday when a tanker truck flipped over on the G15 Highway after colliding with the car ahead of it, according to a news report on Shanghai Television Station.

Thirteen firefighting vehicles responded to the accident. Firefighters in chemical-proof suits spread lime on the ground and sprayed water to dilute or otherwise neutralize the acid, Shen said.

Firefighters hosed down the pavement to push the acid onto a greenbelt to prevent it from flowing into a nearby river, the report said.

The acid killed the plant life and ate away at the highway's metal guard rails, according to the report. The road remained undamaged.

The bureau also closed the water gates on nearby rivers to prevent the acid from contaminating the Huangpu River, the Shanghai Evening Post reported.

Hydrochloric acid can cause external and internal burns, Xu Rong, chief of the Songjiang District Environmental Protection Bureau, told Shanghai Television Station. Fortunately, the spill occurred in an area away from any residential buildings.

The two occupants in the tanker truck were rushed to Shanghai First People's Hospital in Songjiang district, the Shanghai Evening Post reported.

One had suffered burns over 70 percent of his body and was transferred to Ruijin Hospital. The driver of the car was unhurt, though the vehicle suffered some damage.

A witness said the car's driver caused the accident when he slammed on the brakes in front of the truck, which didn't have time to stop.

The accident caused traffic to back up for 5 kilometers on the highway, Shen told the Global Times.

Traffic had returned to normal by 10 pm Tuesday.

The accident was still under investigation Wednesday.