The director of a maximum security laboratory in China's coronavirus ground-zero city of Wuhan has rejected claims that it could be the source of the outbreak, calling it "impossible".

Beijing has come under increasing pressure over transparency in its handling of the pandemic, with the US probing whether the virus actually originated in a virology institute with a high-security biosafety laboratory.

Chinese scientists have said the virus likely jumped from an animal to humans in a market that sold wildlife.

But the existence of the facility has fuelled conspiracy theories that the germ spread from the Wuhan Institute of Virology, specifically its P4 laboratory which is equipped to handle dangerous viruses.

In an interview with state media published Saturday Yuan Zhiming, director of the laboratory, said that "there's no way this virus came from us".

None of his staff had been infected, he told the English-language state broadcaster CGTN, adding the "whole institute is carrying out research in different areas related to the coronavirus".

The institute had already dismissed the theory in February, saying it had shared information about the pathogen with the World Health Organisation in early January.

But this week the United States has brought the rumours into the mainstream, with US Secretary of State Mike Pompeo saying US officials are doing a "full investigation" into how the virus "got out into the world".

When asked if the research suggested the virus could have come from the institute, Yuan said: "I know it's impossible."

"As people who carry out viral studies we clearly know what kind of research is going on at the institute and how the institute manages viruses and samples," he said.

He said that because the P4 laboratory is in Wuhan "people can't help but make associations", but that some media outlets are "deliberately trying to mislead people".

Reports in the Washington Post and Fox News have both quoted anonymous sources who voiced concern that the virus may have come — accidentally — from the facility.

Yuan said the reports were "entirely based on speculation" without "evidence or knowledge".

Authorities in Wuhan initially tried to cover up the outbreak and there have been questions about the official tally of infections with the government repeatedly changing its counting criteria at the peak of the outbreak.

This week authorities in the city admitted mistakes in counting its death toll and abruptly raised the figure by 50 per cent.

Trump warns China of consequences

US President Donald Trump warned China on Saturday that it should face consequences if it was “knowingly responsible” for the coronavirus pandemic, as he ratcheted up criticism of Beijing over its handling of the outbreak.

“It could have been stopped in China before it started and it wasn’t, and the whole world is suffering because of it,” Trump told a daily White House briefing.

It was the latest US volley in a war of words between the world’s two biggest economies, showing increased strains in relations at a time when experts say an unprecedented level of cooperation is needed to deal with the coronavirus crisis.

“If it was a mistake, a mistake is a mistake. But if they were knowingly responsible, yeah, I mean, then sure there should be consequences,” Trump said.

He did not elaborate on what actions the United States might take.

Trump and his senior aides have accused China of a lack of transparency after the coronavirus broke out late last year in its city of Wuhan. This week he suspended aid to the World Health Organisation accusing it of being “China-centric”.

Washington and Beijing have repeatedly sparred in public over the virus. Trump initially lavished praise on China and his counterpart Xi Jinping for their response. But he and other senior officials have also referred to it as the “Chinese virus” and in recent days have ramped up their rhetoric.

They have also angrily rejected earlier attempts by some Chinese officials to blame the origin of the virus on the US military.

Trump’s domestic critics say that while China performed badly at the outset and must still come clean on what happened, he is now seeking to use Beijing to help deflect from the shortcomings of his own response and take advantage of growing anti-China sentiment among some voters for his 2020 reelection bid.

At the same time, however, White House officials are mindful of the potential backlash if tensions get too heated. The United States is heavily reliant on China for personal protection equipment desperately needed by American medical workers, and Trump also wants to keep a hard-won trade deal on track.

Trump said that until recently the US-China relationship had been good, citing a multi-billion agricultural agreement aimed at defusing a bitter trade war. “But then all of a sudden you hear about this,” he said.

He said the Chinese were “embarrassed” and the question now was whether what happened with the coronavirus was “a mistake that got out of control, or was it done deliberately”?

“There’s a big difference between those two,” he said.

Wandering off the topic of the coronavirus, Trump also used the White House briefing to take a swipe at presumed Democratic presidential nominee Joe Biden and his long record on China as a senator and former vice president.

While stressing his own confrontational trade policies toward China, Trump, using his nickname “Sleepy Joe” for his rival, said if Biden wins the White House that China and other countries “will take our country.”

Trump also again cast doubt on China’s death toll, which was revised up on Friday. China said 1,300 people who died of the coronavirus in Wuhan — half the total — were not counted, but dismissed allegations of a cover-up.

The United States has by far the world’s largest number of confirmed coronavirus cases, with more than 720,000 infections and over 37,000 deaths.

Even Dr Deborah Birx, coordinator of the White House coronavirus task force who has steered clear of political aspects of Trump’s contentions briefings, questioned China’s data.

Showing on a chart that China’s death rate per 100,000 people was far below major European countries and the United States, she called China’s numbers “unrealistic” and said it had a “moral obligation” to provide credible information.