All of the 450 people poisoned by a sulphur dioxide leak from a local chemical plant on Monday morning in Xifeng County of southwest China's Guizhou Province were said to be in stable condition last night. They will, however, remain in hospital for further observation.

Sources with the southwest environmental protection supervision center of the State Environmental Protection Administration said yesterday that the nine patients initially considered most at risk were doing well, including Yang Xue, a young girl who was worst affected. All nine were transferred to a municipal hospital in the capital city Guiyang yesterday afternoon.

The majority of those poisoned were students and teachers from two primary schools and one middle school located close to the Sinochem Kailin Chemical Fertilizer Co, where the leak originated.

A doctor surnamed Zou from Xifeng County Traditional Chinese Medicine Hospital said that Heishenmiao primary and middle schools, which are closest to the plant, had the highest numbers of students hospitalized.

"We have received a further 20 patients today, which takes the total number here to more than 100," Zou told China Daily. She said most were suffering from nosebleeds, feeling faint and respiratory problems.

"We have given them medicines and healthy food, and they are all in a stable condition," she said.

Since arriving in Xiaozhaiba Town of Xifeng County on Monday, staff from the southwest center have carried out repair work and tests on facilities at the plant, and adjusted its technical standards.

They also undertook an environmental quality inspection of the area where the leak was found, with particular attention paid to a gas discharge outlet.

A source from the center said: "According to the data we have gathered so far, sulphur dioxide levels over the past two days in the areas around the schools are back within nationally accepted levels."

Authorities were still investigating the cause of the leak, he said.

Huang Yonghui, a local government official, said earlier that the gas had been unable to disperse as quickly as would do normally because of heavy fog on Monday morning.

Although no specific cause for the leak had yet been found, officials with the center said that, "production should be immediately cancelled to avoid poisonous emissions if production facilities appear abnormal".

The plant was told to halt production immediately once the leak was discovered.

A worker at the plant, who asked not to be named, said in a telephone interview that the accident was not as serious as the media had reported. "The students suffered only mild discomfort," he said.

(China Daily April 19, 2007)