The mayor of New York City, Michael Bloomberg, has declared tax-free shopping days to try to boost the city's flagging post-11 September economy.

I encourage you to spend your money - tax free

Mayor Michael Bloomberg

But purchases will only be tax-free for people who shop downtown, where businesses have been hardest hit.

A new study - requested by New York members of the US Congress - has found that the 11 September attacks cost the city $83bn.

As a result, the city is now facing a large budget gap.

No-tax Sunday

Mr Bloomberg announced nine days of tax-free shopping over the next three months.

The first tax-free stretch of three days will start on Sunday, to be followed by further three-day tax holidays in July and August.

Whatever people - tourists or residents - buy in shops and restaurants in Lower Manhattan will be free of the 8.25% sales tax, so long as purchases exceed $500 in value.

Petrol and tobacco are excluded from the plan, however.

The mayor wants people to back patriotism with spending

"From Soho to the Lower East Side, from Chinatown to Battery Park City, I encourage you to spend your money - tax free," said Mr Bloomberg.

People have avoided those parts of the city since the attack on the World Trade Center as downtown has been congested and was heavily polluted by fumes from the burning rubble.

The United States General Accounting Office says that estimate of the costs of 11 September includes the direct destruction of property as well as indirect losses caused by businesses closing.

Even with federal aid and insurance payments, there's still a budget gap of $16bn for the city of New York.

The study - by the investigative arm of Congress - is intended to help understand the pattern of financial loss in New York so as to try to focus economic reconstruction efforts.

"Stores, restaurants and other establishments throughout Lower Manhattan experienced a huge loss in customer traffic, and many are still struggling," said New York state Assembly Speaker Sheldon Silver.