They were told that the Chinese government had not approved the necessary permissions required for them to enter the country.
The World Health Organisation has stated that China blocked its team investigating the origins of the COVID-19 pandemic, from entering the country.
WHO Director-General, Tedros Ghebreyesus, made the announcement on Wednesday, January 6, saying two scientists on the United Nations team had already left their home countries for Wuhan.
But they were told that the Chinese government had not approved the necessary permissions required for them to enter the country.
WHO said the arrangements had been jointly agreed with China in advance.
"I am very disappointed with this news," Tedros told a news conference in Geneva.
"I have been in contact with senior Chinese officials and I have once again made it 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."
Dr. Michael Ryan, executive director of WHO's health emergencies programme said one team member had already returned home while the other was waiting in transit in a third country.
Ryan said the team hoped it was "just a logistical and bureaucratic issue" that could be resolved in "good faith in the coming hours and recommence the deployment of the team as soon as possible."
WHO said it wanted its team of global scientists to have access to key sites to investigate the origin of the virus, first detected in Wuhan in December 2019, and its likely jump from an unidentified host species to humans.
In May, WHO agreed to hold an inquiry into the pandemic after more than 100 countries signed a resolution calling for an independent probe.
In a press briefing on Wednesday January 6, spokesperson for China's Ministry of Foreign Affairs, Hua Chunying, 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.
US President, Donald Trump has repeatedly blamed China for the global pandemic and announced that the US would terminate its relationship with WHO, saying that China had not properly reported information it had about the coronavirus and had pressured WHO to "mislead the world."