Su, a public relations director, told the South China Morning Post that on Wednesday, he saw an immigration officer issue such instructions to a woman.

The woman complied, but looked both amused and annoyed, and said: “Come on, I am more than 50 years old.

A younger woman who was accompanying her was asked to do the same, Su said. She asked: “Am I too fat?”

Both women had entry permits, he said.

The Immigration Department told the Post it was looking into the claims.

The Hong Kong government has been facing pressure from locals to tighten checks on expectant mainlanders who try to enter the city to give birth so that their children will gain right of abode.

Separately, another mainlander told the Post that Hong Kong immigration officers told her to press her stomach as she entered the city in August 2011.

“My friend, who was queueing behind me, was angry and couldn’t believe what she saw.” The woman said she was from Kunshan city in China's eastern Jiangsu province .

Su suggested officers interview the women in rooms rather than in public.

“The procedures were an invasion of the mainland women’s privacy. I’d always thought Hong Kong was a society based on the rule of law that respected individual human rights. But the immigration officers’ conduct really disappointed me,” he said.

As of Friday, Su’s posting had been reposted more than 12,000 times since it went up on Wednesday. More than 5,000 comments followed.

Some web users felt their countrymen had been insulted. “This is absolute discrimination against mainlanders,” one wrote.

But just as many were sympathetic. “It is your choice to go, so put up with it,” one said, urging people to comply with officers.

Ngai Sik-shui, chairman of the Immigration Service Officers Association, said officers would ask suspected pregnant woman to go into a room for inquiries.

In case of doubt, they would ask doctors from the Health Department to check the women, but only Lo Wu and Lok Ma Chau had such doctors, he said.