China's Ministry of Health confirmed Friday that A/H1N1 flu was spreading from cities to rural areas, and from coastal provinces inland.
Domestic cases now made up the majority of new infections instead of those from abroad, said Liang Wannian, deputy director of the ministry's health emergency office.
New domestic cases outnumbered imported ones on 35 days out of the past 42, Liang said.
From Aug. 24 to Sept. 10, the number of domestic cases increased by 3,696, accounting for 94.8 percent of new infections.
Also, cases of large-scale group infection were replacing isolated ones, Liang said.
Since mid June, the mainland had reported 207 cases of large-scale infections, he said. "And the flu is tending to spread from big cities into counties and the countryside."
"The daily number of new infections rose and there were more patients in serious condition," he said.
All 31 provincial areas in the Chinese mainland have now reported A/H1N1 cases. The total had reached 6,968 by Thursday.
"The situation we face is not optimistic," Liang said.
The State Council, or Chinese Cabinet, issued an edict to step up the campaign against the flu on Thursday. It promised to take effective measures such as free vaccination and allowing flexible work hours.
On Wednesday, Beijing began vaccinating about 1.8 million residents aged 60 years and over and students at primary and middle schools.
Yan Jiangying, spokeswomn of the State Food and Drug Administration (SFDA), said the administration would carefully observe the effect of the new vaccines.
Only in June did China's pharmaceutical firms receive seed viruses from the World Health Organization (WHO) to produce A/H1N1 flu vaccines. Clinical tests started in July.
"The vaccine was developed in a very short period but according to proper procedures and in line with laws and rules," Yan said.
The SFDA has asked vaccine producers to report any side effects and negative symptoms and would itself tighten the monitoring, she said.
"Any vaccine is likely to cause side effects," she said.
Two pharmacy firms have received SFDA warrants for flu vaccines. The SFDA was still processing other firms' applications, Yan said.
"We will strictly supervise production and storage of the vaccines," she said.
Under State Council guidelines, the Health Ministry is busy preparing for epidemic prevention and control during coming National Day celebrations
The guideline will also boost work at vulnerable venues such as schools, Liang Wannian said.
Among large-scale group infections, about 86.5 percent have occurred in schools or activities related to schools, Liang said.
Liao Wenke, a senior official with the Ministry of Education, said preschool facilities and schools were required to be fully prepared to deal with the A/H1N1 virus.
They were required to educate every student about how to prevent infection and teachers had been asked to update all students' health information every day, Liao said.
"Schools are to avoid big gatherings, especially indoors," he said.
They will also prepare quarantine facilities for flu patients and those having close contact with them, he said.
"If a school reports a serious outbreak, it will be closed temporarily under the supervision of local governments," he said.