A third Canadian national held in China in recent weeks is undergoing "administrative punishment" for working illegally, Beijing has said, amid an ongoing diplomatic row between the two countries.

Chinese state security agents last week detained two Canadians, former diplomat Michael Kovrig and businessman Michael Spavor, saying they were suspected of endangering state security.

The detentions of the Canadians followed the 1 December arrest in Vancouver of Meng Wanzhou, chief financial officer of the Chinese telecommunications giant Huawei Technologies Co Ltd.

Ms Meng was arrested at the request of the US, which is engaged in a trade war with China.

Chinese Foreign Ministry spokesperson Hua Chunying identified the third Canadian as Sarah McIver, who was serving "administrative punishment" due to "illegal employment". She did not elaborate.

"What I can tell you is that China and Canada are maintaining clear consular communication," Ms Hua told a daily news briefing.

When asked if Ms McIver's case was connected to that of Mr Kovrig and Mr Spavor, Ms Hua pointed out the nature of the cases were different, given the other two were accused of endangering national security.

Ms Hua referred further questions on Ms McIver to the Ministry of Public Security. That ministry did not immediately respond to requests for further comment.

The Canadian government has not identified the third Canadian, though Canadian media has said the person is Ms McIver and said she was an English teacher being held because of "visa complications".

Canadian Prime Minister Justin Trudeau urged caution on Wednesday and said he would not be "stomping on a table" after China detained the third Canadian.

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Mr Trudeau said he was asking China for more information on the detentions.

He said the latest incident was "a very separate case" from the other two.

The Canadian government has said several times it saw no explicit link between the arrest of Ms Meng, the daughter of Huawei's founder, and the detentions of Mr Kovrig and Mr Spavor.

But Beijing-based Western diplomats and former Canadian diplomats have said they believed the detentions were a "tit-for-tat" reprisal by China.

China has demanded Ms Meng's immediate release and summoned the Canadian and US ambassadors to complain about the case.

Ms Meng is accused by the US of misleading multinational banks about Iran-linked transactions, putting the banks at risk of violating US sanctions.

She was released on bail in Vancouver, where she owns two homes, while waiting to learn if she will be extradited to the US. She is due in court on 6 February.