China has accused detained Canadian citizen Michael Kovrig of stealing state secrets that were passed on to him from another detained Canadian, Michael Spavor, in what is likely to further ramp up tension between Ottawa and Beijing.

Key points: Michael Korvig and Michael Spavor were arrested in December last year

Michael Korvig and Michael Spavor were arrested in December last year Their detention followed the high-profile arrest of Huawei CFO Meng Wanzhou

Their detention followed the high-profile arrest of Huawei CFO Meng Wanzhou China was angered by Canada's approval of extradition proceedings against her

Businessman Mr Spavor, who worked with North Korea, and former diplomat Mr Kovrig were picked up in early December, shortly after Canada arrested Huawei's chief financial officer Meng Wanzhou, who faces extradition to the United States.

China has repeatedly demanded Ms Meng be released, and reacted angrily last week when Canada's Government approved extradition proceedings against her.

The ruling Communist Party's Central Political and Legal Affairs Commission said Mr Kovrig had often entered China using an ordinary passport and business visas, "stealing and spying on sensitive Chinese information and intelligence via a contact in China".

Huawei global chief financial officer Meng Wanzhou is suing the Canadian Government over her arrest. ( Supplied: Huawei.com )

"Spavor was Kovrig's main contact and provided him with intelligence," the commission added, without giving details.

Mr Kovrig severely violated Chinese laws, and China will start the next judicial proceedings in due course, it said.

"China is a country with rule of law and will firmly crack down on criminal acts that severely undermine national security."

Mr Kovrig works for the International Crisis Group (ICG), which focuses on conflict resolution and has denied any involvement in espionage.

Canada's Foreign Ministry did not immediately respond to a request for comment. The ICG said it had heard nothing official about any charges.

"Michael's work for Crisis Group has been entirely transparent and in the open," spokesman Karim Lebhour said.

"Vague and unsubstantiated accusations against him are unwarranted and unfair."

China has accused the US of attempting to undermine Huawei's success. ( AP: Andy Wong )

Detainees may be under pressure to 'confess'

While Canada says China has made no specific link between the detentions and Ms Meng's arrest, experts and former diplomats say they have no doubt it is using the cases of the two men to pressure Canada.

Canadian diplomats have been allowed to see the two men. However, sources familiar with the case have said Mr Kovrig has not been allowed access to lawyers or family members, unlike Huawei's Ms Meng.

It is not clear what conditions Mr Spavor is being held in.

David Mulroney, a former Canadian ambassador to China, said the detainees would come under increased pressure to talk about people they had met.

"They'll be told that if they confess to something they may be able to expect a degree of leniency," he told the Canadian Broadcasting Corp.

"They'll also probably be asked to see if they can put pressure on Canadian officials who visit them to see if they can secure the release of Ms Meng."

China has said it is fully guaranteeing both men's lawful rights. Mr Kovrig also holds Hungarian citizenship.

Canada arrested Ms Meng on December 1 as she was changing planes in the city of Vancouver.

She was detained at the request of the United States, which has filed sweeping charges against Huawei and Ms Meng that paint the company as a national security threat.

China's arrest of the two Canadians has been widely seen as a response to Canada's arrest of Meng Wanzhou. ( AP, The Canadian Press: Darryl Dyck )

Ms Meng has been charged with bank and wire fraud to violate US sanctions against Iran.

She is free on bail and denies the charges against her.

Ms Meng is suing the Canadian Government, as well as its border agency and the police force, alleging they detained, searched and interrogated her before telling her she was under arrest.

Separately, Huawei plans to announce a lawsuit against the US Government on Thursday on grounds related to a defence bill, a source with knowledge of the matter said.

Reuters