The company's assistant general manager, Leung Kong-lan, said: 'The passports were stolen just as our Thailand staff had completed the check-in procedures and was ready to return the documents to the tourists.

'The Hong Kong tour guide was taking care of the tourists at that time.' She said they had reported the case to the police and the British embassy in Bangkok to arrange for emergency travel documents.

A Thai tourist police officer said a member of the group called the station to report the missing documents, but the conversations lasted no longer than a few minutes.

'As soon as we questioned whether they were really stolen and said they must come in, they stopped talking and now we don't know what happened,' the officer said.

It is understood that this was the second time this week the British embassy has had to help tourists who lost passports at Bangkok's Don Muang airport. The other case involved a Briton.

Ms Leung said: 'It happened so quickly.

'I think security at the airport should be stepped up and we would remind our staff about the problem.' She said the tourists were taken sightseeing during their extra stay in Bangkok and all the expenses would be paid by the company.

'We have also informed their families and companies to arrange for extra leave for their staff,' Ms Leung said.

Ms Leung said she believed the group could return to Hong Kong at the earliest today after clearing the procedures with the embassy and Thai's authorities.

The 19 Hong Kong people included 18 British National (Overseas) passport holders. For the holder of a Certificate of Identity, the embassy said they had to check the tourist information with Hong Kong's Immigration Department before issuing the emergency passport.