China's largest city and the host of a dozen Olympic football matches started tightening security over the weekend at airports and train stations, according to reports in state-run media Monday.

Surveillance systems also are being installed on Shanghai's subway trains, a report said.

The measures go along with increased security in Beijing, where the Olympic Games will begin Aug. 8. The Chinese government is worried about foreign terrorist plots as well as political protests from domestic critics such as Uighurs in the restive western province of Xinjiang and Tibetans.

Also on Monday, the state-run China Daily newspaper cited the Olympics security chief Ma Zhenchuan as saying that a radical Islamic group based in China's predominantly Muslim Xinjiang region "poses a real threat to the Beijing Olympics."

Bags at Shanghai's Pudong and Hongqiao airports were being searched at entrances to terminals for explosive, flammable, biochemical or radioactive materials, the Shanghai Daily newspaper reported.

The newspaper said passengers at Shanghai South Railway Station will go through a luggage check before entering the station, and only passengers will be allowed on the platforms.

Work to install surveillance systems on every subway train has started, but it's not clear how long it will take, Shao Weizhong, a deputy manager of Shanghai Metro Operation Co., told Shanghai Daily.

Shanghai will host nine men's football matches and three women's matches, and more than 440,000 tickets have been sold so far, Vice Mayor Zhao Wen told the state-run Xinhua News Agency in a report Sunday.

Ma, the Olympics security chief, said investigations have found that the East Turkestan Islamic Movement, or ETIM, has been plotting terror attacks on games venues. "It's not imaginary," he was quoted as saying in the English-language China Daily.

Radicals among Xinjiang's indigenous Turkic Uighur people have been fighting Chinese rule for decades. Earlier this month, Chinese authorities said they had detained 82 suspected Islamic terrorists and separatists in the first half of the year across Xinjiang.

Most experts say the actual threat to the Beijing Games from terrorism is low, although the event has become a magnet for critics of the government, ranging from free-speech advocates to activists over Tibet and Sudan's troubled Darfur region. China has prepared an anti-terror force of nearly 100,000 commandos, police and troops for the Olympics.