An international team of scientists led by the World Health Organization arrived on Thursday in China’s central city of Wuhan to investigate the origins of the novel coronavirus that sparked the pandemic.

The group arrived late in the morning on a budget airline from Singapore and was expected to head into two weeks of quarantine. They had been set to arrive earlier this month, and China’s delay of their visit drew rare public criticism from the agency’s chief.

The team left the airport terminal through a plastic quarantine tunnel marked “epidemic prevention passage” for international arrivals and boarded a cordoned-off bus that was guarded by half a dozen security staff in full protective gear.

Team members did not speak to reporters, although some waved and took pictures of the media from the bus as it departed.

The United States, which has accused China of hiding the extent of its initial outbreak a year ago, has called for a “transparent” WHO-led investigation and criticised the terms of the visit, under which Chinese experts have done the first phase of research.

The team arrived as China battles a resurgence of cases in its northeast after managing for months to nearly stamp out domestic infections.

Peter Ben Embarek, the WHO’s top expert on animal diseases that cross to other species, who went to China on a preliminary mission last July, is leading the 10 independent experts, a WHO spokesman said.

Hung Nguyen, a Vietnamese biologist who is part of the team, told Reuters that he did not expect any restrictions on the group’s work in China, but cautioned the team might not find clear answers.

After completing quarantine, the team will spend two weeks interviewing people from research institutes, hospitals and the seafood market in Wuhan where the new pathogen is believed to have emerged, Hung added.

The team would mainly stay in Wuhan, he told Reuters in an interview on Wednesday during a stopover in Singapore.

Last week, WHO director-general Tedros Adhanom Gheybreyesus said he was “very disappointed” that China had still not authorised the team’s entry for the long-awaited mission, but on Monday, he welcomed its announcement of their planned arrival.

“What we would like to do with the international team and counterparts in China is to go back in the Wuhan environment, re-interview in-depth the initial cases, try to find other cases that were not detected at that time and try to see if we can push back the history of the first cases,” Ben Embarek said in November.

China has been pushing a narrative via state media that the virus existed abroad before it was discovered in Wuhan, citing the presence of the virus on imported frozen food packaging and scientific papers claiming it had been circulating in Europe in 2019.

“We are looking for the answers here that may save us in future - not culprits and not people to blame,” the WHO’s top emergency expert, Mike Ryan, told reporters this week, adding that the WHO was willing to go “anywhere and everywhere” to find out how the virus emerged.

Team member Marion Koopmans, a virologist at Erasmus University Medical Center in the Netherlands, said last month it was too soon to say whether the SARS-CoV-2 virus had jumped directly from bats to humans or had an intermediate animal host.

“At this stage what I think we need is a very open mind when trying to step back into the events that led eventually to this pandemic,” she told reporters.