Assistant Principal Immigration Officer Chow Kwok-chuen said marriages of convenience were mostly resorted to by women who failed to have the necessary skills levels to qualify for residency in Hong Kong.

He said most of the women came from low income countries in the region and were forced to ''resort to other means of entry''.

Mr Chow refused to name which nationalities were most commonly involved in the scam. However, it is widely known that women seeking to marry Hong Kong citizens for the right to live here are generally from the Philippines and Thailand.

Some of the women are forced to work as prostitutes to pay off the debts they have incurred in coming to Hong Kong to take part in a sham marriage.

''In some cases, we have found these people getting married don't even know each other,'' Mr Chow said.

He said it was widely known that groups in Hong Kong and overseas were organising marriages of convenience, but little could be done to identify the ringleaders.

''These people are working very much behind the scenes.'' Mr Chow said the racketeers were training people in what to say when they were questioned by Hong Kong immigration authorities.

''The racketeers are becoming more professional and upgrading their efforts to match the Immigration Department, which has also been increasing its efforts to stop these people.'' Mr Chow said the fee to arrange a marriage of convenience was sometimes paid by the applicant's family and then split between the husband and the broker making the arrangements.

In the past two years, the Immigration Department has received about 18,000 applications from spouses seeking to join their partners, who were Hong Kong residents.

Of that 18,000, about 1,200 applications were refused.

Mr Chow said it was almost impossible to monitor applicants after they had received approval for residency.

''Like all foreigners they must re-apply for residency after one year here but it is hard to know if the marriage that took place was ever genuine.

''We would like to be more pro-active and if someone who took part in the scam was able to provide us with enough evidence we would certainly consider offering that person an indemnity from prosecution.

''The best way to identify possible sham marriages is to look at the people quite closely and interview them both. If they speak different languages and come from different cultural backgrounds we tend to start asking questions.'' He said in some instances when a couple were split up and spoken to separately by immigration officers it was discovered that they knew little or nothing about each other.

Mr Chow said another immigration issue his department was examining involved passports of convenience being sought by mainland Chinese attempting to bypass the one-way permit system allowing 105 people per day into Hong Kong.

Although not illegal, the Hong Kong Government has imposed a restriction on people using this method, requiring that they must have lived outside of China for at least two years before seeking residency.

in Hong Kong.

Passports can be readily bought in some South American and African nations keen for foreign currency.