Mr Joseph Tung, executive director of the Travel Industry Council of Hong Kong, said the number of tourists affected might be higher than 500 as they could only contact those travelling in commercial tour groups.
'The tour groups are all stranded in the city. The transport network in Bangkok is completely paralysed,' he said.
All the tourists were safe and were 'staying at hotels in the city centre, which is relatively peaceful,' he said.
The immigration department said it had received 158 enquiries and eight requests for assistance in relation to the situation in Thailand.
The Hong Kong Airport Authority said that a total of 29 flights scheduled to fly between Hong Kong and Bangkok had been cancelled up to 0500 GMT (1.00 pm Singapore time).
Mr Tung said two Hong Kong tour groups currently in Mumbai were safe and had been accounted for.
Officials say at least 100 people were killed and hundreds more wounded in coordinated gun and grenade attacks across India's financial capital that began late on Wednesday.
'Our tourists in Mumbai are safe, and some of them are already leaving the city for other places in India,' he said.
The immigration department said that at 0700 GMT (3.00 pm Singapore time) it was still trying to ascertain the safety of Hong Kong people travelling in Mumbai.
Hong Kong carrier Cathay Pacific said all its scheduled flights between Hong Kong and Bangkok have been cancelled, while those to Mumbai remain unaffected. -- AFP