The Chinese mainland is expected to see more serious and even fatal cases of the A/H1N1 virus as the weather cools and people return to work after the just-ended eight-day National Day holiday, a Health Ministry spokesman said Saturday.

"China's situation is still rather grim," Deng Haihua, spokesman with the ministry, told a press conference.

His words came just days after the mainland reported its first death from the disease, an 18-year-old woman in Maizhokunggar County, in Tibet's Lhasa City, who died on Oct. 4.

The virus was spreading from the eastern and southern parts of the country to the west and the north, and from urban areas to the countryside, Deng said.

"With people returning to their work places after the holiday, we are looking at a strong possibility of mass outbreaks of the disease," he said.

The mainland is expected to see "constantly" more serious and even fatal cases caused by the flu virus, he added.

By Friday, the mainland had reported a total of 22,830 cases of A/H1N1, more than 17,000 of them reported in September alone.

Thirteen patients had been reported to be seriously ill, but nine of them had recovered. The others were still being treated, said Deng.

China was the first country in the world to issue a production license for vaccines against the A/H1N1 flu last month.

But all the vaccines so far produced in the country were stocked by the state and were not on the market, Deng said.

More than 300,000 people had been given the vaccine, of whom 150 showed adverse reactions including local swelling and pain, fever, vomiting and fatigue, he said.

"Most of the adverse drug reactions reported were mild," Deng said. "Generally speaking, our inoculations with the A/H1N1 flu vaccine have been successful."