The World Health Organization (WHO) said that China has blocked the arrival of a team investigating the origins of the coronavirus pandemic, in a rare rebuke from the UN agency.

WHO Director-General Tedros Adhanom Ghebreyesus said two scientists on the United Nations team had already left their home countries for Wuhan when they were told that Chinese officials had not approved the necessary permissions to enter the country. The arrangements had been jointly agreed with China in advance.

"I am very disappointed with this news," Tedros told a news conference in Geneva on Tuesday. "I have been in contact with senior Chinese officials and I have once again made clear that the mission is a priority for WHO and the international team."

Tedros said WHO was "eager to get the mission underway as soon as possible" and that he had been given assurances that Beijing was speeding up the internal procedure for "the earliest possible deployment."

Spokesperson for China's Ministry of Foreign Affairs, Hua Chunying, during a press briefing on Wednesday, said China had "always held an open, transparent and responsible attitude" on tracing the origin of the virus.

Hua said that China had previously welcomed WHO experts into the country and said that the UN investigation team and Chinese experts have "maintained frequent interactions" including four video meetings between October and December.

"In order to ensure that the international expert group that comes to China can work smoothly, it is needed to fulfill the necessary procedures and make relevant specific arrangements. The two sides are still negotiating about this," said Hua.

Marion Koopmans, a Dutch virologist who heads the Erasmus Medical Centre's Department of Viroscience in Rotterdam and is part of the investigation team heading to China, said that they were "ready to go."

Koopmans said that they have been told nothing is off limits while in China and said the team will be working in collaboration with their Chinese colleagues "looking at the data, talking to people with expertise, and concluding from what's been done, and what can be built on."

She said, "We really need to have patience and not judge. It's meticulous work, it will take time," Koopmans said. The United States and Australia have led the charge in criticizing China's handling of the initial stages of the pandemic, accusing Beijing of downplaying its severity and preventing an effective response until too late”.

As countries around the world struggle with new infection surges and outbreaks, China appears to be rebounding. Last month, the country posted positive economic growth for the second quarter in a row.

Foreign Minister Wang Yi praised China's anti-pandemic efforts at home and abroad, saying that the country "launched an emergency global humanitarian campaign" and "helped build consensus on a global response to Covid-19."

The WHO team that prepared to embark, Chinese officials and state media have questioned the virus' origins, saying "more and more research suggests that the pandemic was likely to have been caused by separate outbreaks in multiple places in the world," according to Wang.

On Monday, the reports circulated on Chinese social media that the virus had been detected on auto part packaging in multiple cities, including from foreign brands.

It has been for months, China has been testing and disinfecting frozen products imported from overseas, over fears the virus could reenter the country that way, even as experts remain skeptical about this as a potential source of infection.

WHO says it is "highly unlikely that people can contract Covid-19 from food or food packaging," and the US Centers for Disease Control and Prevention (CDC) says the risk is "thought to be very low." Both insist there is no evidence of such transmission, and countries have even threatened to bring a case against China at the World Trade Organization over import restrictions.