China has begun using anal swabs to test those it considers to be at high risk of contracting Covid-19, state TV has reported.

Officials have taken anal swabs from residents of neighbourhoods with confirmed Covid-19 cases in Beijing last week, according to state broadcaster CCTV.

Those in designated quarantine facilities have also received anal swab tests.

To collect test samples, the swab needs to be inserted about 3-5cm into the rectum and rotated several times.

After completing the motion twice, the swab is removed before being securely placed inside a sample container. The whole procedure is said to take about 10 seconds.

The mass testing in the capital was sparked after a 9-year-old tested positive for the virus last week.

Since January 17, more than three million residents in three Beijing districts have received coronavirus testing in a bid to stem the contagion, authorities said.

More than 1,000 staff and students at the infected young patient's school also underwent a variety of nucleic acid tests including the anal swabs, reported state media.

Anal swabs have been used in China to test for Covid-19 since last year, but the method is mainly used in key groups at quarantine centres because of its inconvenience, according to a Chinese disease control expert.

Speaking to state broadcaster CCTV on Saturday, Li Tongzeng from Beijing You'an Hospital said that traces of the virus linger longer in the anus or excrement than those samples taken from throat and nasal swabs.

"We found that some asymptomatic patients tend to recover quickly. It's possible that there will be no trace of the virus in their throat after three to five days," Li noted.

"But the virus lasts longer from the samples taken from the patient's digestive tract and excrement, compared to the ones taken from the respiratory tract.

"If we conduct anal swabs for nucleic acid testing, it would increase the detection rates of patients and lower the chance of a missed diagnosis," the expert claimed.

Arrivals into the China must have multiple negative test results and quarantine for at least 14 days in a designated hotel on arrival, with many cities and regions imposing additional home observation requirements.

As of Wednesday, China has reported a total of 89,272 confirmed infections. Its death toll rose by one to 4,636 following an additional fatality on Monday.