US taxpayers living in Asia have until 23 September to register their untaxed offshore assets with the US Internal Revenue Service or else face prosecution, said international law firm Withers.

"It is imperative that US taxpayers in Asia understand that, if they have undeclared offshore accounts, their chances of being prosecuted by the US Government will increase significantly after the deadline passes," said Withers Hong Kong partner Kurt Rademacher, in a statement.

Violators will not only face financial penalties, but also run the risk of arrest upon entry into the US.

The IRS and other revenue agencies of governments such as the UK are trying to crack down on citizens they say are hiding money in offshore financial centres. Through a mixture of threats and tax amnesties, such authorities are trying to recover revenues.

"This doesn't just mean no more holidays in the United States - it could prevent people from visiting children or relatives in the country, or receiving urgent medical treatment," Mr Rademacher adds.

The law firm notes that presently there are around 60,000 US passport holders based in Hong Kong, 7 to 8,000 in Malaysia, and 15,000 in Singapore, just to name some. Hong Kong and Singapore have reportedly expressed willingness to cooperate with US authorities on the matter.

The new IRS guidelines were issued in 23 March.