'We want to convey our idea to the world that Tibet is part of China and that all Chinese people support the Olympics. I hope that when many foreigners come to China and see these T-shirts, they will know the truth,' said one seller, who goes by the internet name of Fu Naiyun and works for an internet company in Nanjing .

Some internet postings have urged people to wear the T-shirts on the May 1 holiday as a protest against western critics, or when the Olympic torch passes through their cities from next month through August.

Although state media and the central government appear to be trying to cool nationalist sentiment, simply wearing T-shirts is thought unlikely to invite a crackdown.

Fu said his design was so popular that he had ordered a second batch from the manufacturer, but he was selling the shirts at cost for only 19 yuan (HK$21.20) apiece.

'We made about 200 T-shirts at first but raised the number to 1,500 because of demand,' he said.

Another seller said he and his friends had originally given away the shirts in downtown Beijing but were stopped by police, so he started selling them for less than 20 yuan.

'Some netizens, most of them from Tsinghua University, found that holding the national flag was not an effective way to show our patriotism, so we decided to make eye-catching T-shirts,' he said.

They had sold about 5,000 shirts, at a rate of 500 a day, he claimed. One design calls for people to boycott French retailer Carrefour on May 1.

'I recall that when we wore the T-shirts and went to the university canteen last time, some foreigners were very surprised and kept their eyes on us for a long time, so I think it should be effective,' the seller said.

Additional reporting by Lilian Zhang