Research showed about three to 14 percent of the former patients were diagnosed with the virus once more after being given the all-clear, the Daily Mail reported.

The news came as experts feared that China is facing a second outbreak due to the increasing number of imported cases as well as the 'silent carriers' who show no symptoms.

Millions of residents of Hubei, the former centre of the pandemic, can now leave the province after officials lifted a two-month draconian lockdown.

Doctors in one hospital in Wuhan found that five of the 147 patients in a study tested positive again after recovery, Wang Wei, director of the city's Tongji Hospital, told the state broadcaster CCTV yesterday.

Meanwhile, 14 percent of those who recovered were diagnosed with the pathogen later in southern China's Guangdong Province, said Song Tie, deputy director of the provincial Centre for Disease Control and Prevention.

In the study conducted by the Wuhan medics, the recovered patients showed no symptoms after testing positive again. But the researchers found no evidence that they became infectious after recovery as their family members all tested negative.

Guangdong officials also suggested the people in close contact with such recovered patients weren't infected by them.
Medical experts have raised questions about if nucleic acid tests are reliable in detecting traces of the virus in some of the recovered patients.

"It's possible that these recovered patients tested negative before because of false results," Mr Wang added. 'The accuracy of a nucleic acid test is 30 to 50 percent.

The chief doctor said it was crucial to closely monitor recovered patients and put them under two-week quarantine after discharge.

"Our sample size for this study was relatively small," said the hospital director. "We are planning to carry out large-scale research among local communities in Wuhan soon."

Other reports suggested that the number of people infected with coronavirus who show no or delayed symptoms could be as high as one-third of those who test positive for the disease.

According to classified Chinese government data seen by the South China Morning Post, the true scale and of the hidden number of these 'silent carriers' could be higher than first thought.

It said by the end of February more than 43,000 people had tested positive for coronavirus in China without showing symptoms and were quarantined but not counted in official figures, which stood at 80,000 at the time.