China said Tuesday it was expelling Canada's consul in Shanghai, in a tit-for-tat move after Ottawa announced it was sending home a Chinese diplomat accused of trying to intimidate a lawmaker.

The expulsions have plunged the two nations into a fresh diplomatic row after years of souring relations.

They follow an outcry in Canada over allegations that Chinese intelligence had planned to target MP Michael Chong and his relatives in Hong Kong with sanctions for sponsoring a motion condemning Beijing's conduct in the Xinjiang region as genocide.

In response, Canadian Foreign Minister Melanie Joly said Toronto-based Chinese diplomat Zhao Wei -- who allegedly played a role in the scheme -- would have to leave the country.

Canada, she said, would "not tolerate any form of foreign interference in our internal affairs".

The Chinese foreign ministry on Tuesday condemned the decision to expel Zhao, and said it had ordered Canadian consul Jennifer Lynn Lalonde to leave the country by May 13.

"As a reciprocal countermeasure in reaction to Canada's unscrupulous move, China decides to declare Jennifer Lynn Lalonde, consul of the Consulate General of Canada in Shanghai persona non grata," the ministry said in a statement.

A single police car was parked outside the Shanghai office building where the consulate is based, AFP journalists saw.

Inside, appointments appeared to be running as normal, and staff at reception said they were unaware of Tuesday's developments.

Neither Canada's foreign ministry nor its embassy in Beijing replied to requests for comment from AFP.

"We remain firm in our resolve that defending our democracy is of the utmost importance," Joly said Monday, adding that foreign diplomats in Canada "have been warned that if they engage in this type of behaviour, they will be sent home".

- 'Playground for interference' -

Prime Minister Justin Trudeau has faced growing pressure to take a hard line on China following revelations in recent months that it sought to sway Canada's 2019 and 2021 elections in his party's favour.

Relations between Beijing and Ottawa have been tense since Canada's 2018 arrest of a top Huawei executive and the detention of two Canadian nationals in China in apparent retaliation.

All three have been released, but Beijing has continued to blast Ottawa for aligning with Washington's China policy, while Canadian officials have regularly accused China of interference.

After China's ambassador was summoned last week over the latest interference allegations, Beijing on Friday slammed what it called "groundless slander and defamation" by Canada.

The Chinese foreign ministry insisted the scandal had been "hyped up" by Canadian politicians and the media.

On Monday, Chong told reporters in Ottawa: "It shouldn't have taken the targeting of a member of Parliament to make this (expulsion) decision."

"We have known for years that the PRC is using its accredited diplomats here in Canada to target Canadians and their families," he said, using an acronym for the People's Republic of China.

He said Canada has become "a playground for foreign interference," including the harassment of diaspora communities.