"At the beginning of last week, we were no longer able to get any multiple entry visas for anyone," Daryl Bending, from Concorde Travel in Hong Kong, said.
"The main reason is to do with the Olympics, and we expect that after the Olympics things will return to normality," he said.
Sunrise International Travel Company, also based in Hong Kong, said on its website that it would be unable to get hold of multi-entry visas - that are valid for between six months and three years - until October.
Single-entry and double-entry visas, valid for up to three months, are still available, the agents said.
A travel agent with a tour company in Singapore said the move took effect March 27 and China would not be issuing multi-entry visas until further notice.
Bending said some people had already cancelled planned trips to China when they were faced with the restrictions.
Andrew Work, executive director of the Canadian Chamber of Commerce in Hong Kong, said the ban would cause problems for foreigners living and working in Hong Kong, a report said.
"This is a real hassle for foreign small and medium-sized business owners - it's bound to slow down business," Work told the Sunday Morning Post.
Short-stop visas that were available for some nationalities, including Australians, at the border with the southern Chinese manufacturing hub of Guangdong province, had also been stopped, Bending added.
The border city of Shenzhen is a popular day trip destination for Hong Kong residents looking for shopping bargains.
No one was immediately available for comment from the Chinese foreign ministry in Hong Kong or in Beijing.
Hong Kong, despite being a part of China, is run on a different legal and visa systems since it was returned by colonial power Britain in 1997.