Patriotic Americans are continuing to snap up red, white and blue T-shits and flags at such a rate that many manufacturers and retailers are struggling to keep up with demand, industry chiefs have reported.

Millions of T-shirts and sweaters featuring the colours of the American flag have flown off shop racks and shelves since the terrorist attacks on September 11 devastated New York and the Pentagon.

The country's largest retailer, Wal-Mart Inc, has sold hundreds of thousands of patriotic T-shirts over the past week, while Gap Inc's Old Navy stores begun limited production of the American flag tees they sell every fourth of July - with the proceeds going to charity.

A Wal-Mart spokesman said: "It seems we are able to keep up, but the sell-through is very quick. If we get in a large lot, it's safe to say half of it is gone in a couple of days."

The surge in demand has led to suppliers working round the clock to meet production deadlines. They include North Carolina-based Liberty Screenprint Inc which has churned out more than 300,000 American flag T-shirts since the attacks.

"During the Gulf War, we did quite a few T-shirts, but nothing that would come close to what we're seeing now," said co-owner Steve Carlson.

"This is unprecedented demand. Not only are we printing these things, we're folding them and bagging them, counting for accuracy, putting on the UPC labels, and shipping them out. It's a pretty massive undertaking."

Sara Lee Corp's Hanes unit has also seen demand for its plain T-shirts jump 30 per cent to 40 per cent since the attacks as printers rush to slap their red, white and blue designs onto the blank shirts.