'They come from Henan, Hunan and Jiangxi, the poorer provinces. Some bring along religious souvenirs and texts they pinch from the monasteries,' a police source said.

The conmen target public housing estates and beg door to door, he said.

'From the cash we have found on them we have discovered they were making over $50,000 a month,' the source said.

'But we do not rule out the possibility that they have already sent money back to the mainland because they realise they will eventually get caught.' Some were repeat offenders, he said.

'There's one who has been caught by us 12 times in the past 12 months. But we cannot take action unless the public reports to us or we catch them in the act,' the source said.

'Otherwise, what we can do is to repatriate them back to where they came from.' The Hong Kong Buddhist Association has warned the public not to donate cash to people simply because they are dressed as monks or nuns.

'Mainland monks and nuns have to go through certain procedures for their religious activities here,' the association's chief executive, Chiu Sze-yin, said.

He said information on monks and nuns was filed with the association and was used to apply for special permits from the Immigration Department.

'Normally, the imported religious activities would not include alms begging. The public should question the monks and nuns about the religious groups they belong to and ring us if they have a query,' Mr Chiu said.

'If the public wishes to donate money, they can ask the monks and nuns for the name of their religious groups and send money by cheque. An official receipt will be sent back to the donors for tax exemption.' Two years ago, flocks of mainlanders disguised as monks were smuggled across the border to cheat people by selling Buddhist sutras, images and beads stolen from mainland temples.