About 11,000 tons of sulfuric acid leaked from a chemical plant in southern Sweden on Friday, forming a poisonous gas cloud over the city of Helsingborg that forced citizens to stay indoors for four hours, officials said. 

Officials said at least 13 people were injured, but none seriously. No fatalities were reported.

The acid leaked out shortly after 4 AM (0300 GMT) from the Kemira Kemi factory in central Helsingborg, a port city on Sweden's southwestern coast 600 kilometers south of the capital, Stockholm.

Helsingborg is separated from Denmark by a narrow strait and lies just 60 kilometers east of the Danish capital, Copenhagen.

Large sections of the city were blocked off to traffic Friday morning, and ferry traffic to Denmark was canceled. By 11 AM, most streets were reopened, except for the blocks surrounding the chemical plant.

Residents had initially been warned to stay indoors and not go outside, but by the morning, the cloud was beginning to evaporate and the danger lessening.

Carina Mohlin, director of the Helsingborg Lasarett hospital, said six factory employees were taken to the hospital, some with teary eyes and respiratory problems, but none with serious injuries.

Two police officers and five others were also taken in with similar symptoms, but all 13 had been cleared from the hospital by 11 AM (1000 GMT), she said.

"They were taken through a decontamination tent," Mohlin said. "They were all nearby when it happened, and were coughing."

No other injuries were reported.

Christina Didner, a pharmacist with the Sweden Poisons Information Center said exposure to low concentrations of sulfuric acid "could cause teary eyes, an irritated nose and throat and some coughing. If you notice these symptoms, just go back inside."

Ronny Moeller, a spokesman for the Helsingborg Rescue Service, said the leak was probably caused by a broken water pipe that softened the ground under the tank holding the acid. The unstable soil then apparently caused the tank to crack, he said.

Kemira Kemi officials could not immediately be reached for comment, but the company issued a statement saying its delivery of sulfuric acid would resume shortly.

Moeller said the sulfuric acid leaked into a nearby harbor, mixing with the water and creating a large gas cloud that drifted out over the water.

"It's a good thing the wind was blowing toward the strait," he said. Had it blown toward the city, "we don't know what would have happened."

Rescue officials will work through the day to pump the remaining acid into the water, which environmental authorities said was the best way to decontaminate the area.

(China Daily February 5, 2005)