The head of the World Health Organization said on Tuesday that he is “disappointed” Chinese officials have not finalised the permissions to allow a team of experts into China to examine the origins of Covid-19.

WHO Director General Tedros Adhanom Ghebreyesus, in a rare critique of Beijing, said members of the international scientific team began departing from their home countries over the last 24 hours as part of an arrangement between WHO and the Chinese government.

“Today, we learned that Chinese officials have not yet finalised the necessary permissions for the team’s arrival in China,” Tedros said during a news conference in Geneva.

“I’m very disappointed with this news, given that two members had already begun their journeys and others were not able to travel at the last minute, but had been in contact with senior Chinese officials,” he said.

Tedros said he “made it clear” that the mission was a priority for the UN health agency, and that he was “assured that China is speeding up the internal procedures for the earliest possible deployment”.

“We are eager to get the mission under way as soon as possible,” he said.

The experts drawn from around the world are expected to visit the city of Wuhan, which is suspected to be the place that the coronavirus first emerged over a year ago.

Dr Michael Ryan, the WHO’s emergencies chief, said the deployment had been expected to start on Tuesday, but that the needed approvals had not yet been granted, including for visa clearances.

The UN health agency came under searing criticism from US President Donald Trump and other US officials over its alleged deference to and excessive praise of China’s handling of the initial outbreak of the novel coronavirus, which has since swept the globe.

Ryan said Tedros had “taken immediate action” and spoken with unspecified senior Chinese officials and “has fully impressed upon them the absolute critical nature of this”.

“We hope that this is just a logistical and bureaucratic issue that can be resolved very quickly,” Ryan added.

The WHO chief met Chinese President Xi Jinping as the pandemic was emerging early last year.