China Thursday reported small coronavirus outbreaks driven by the Delta variant in three provinces as a cluster linked to an eastern airport spreads despite mass testing and a vaccination drive.

The flare-up, which began after nine workers at the Nanjing airport tested positive on July 20, has seen 171 cases detected in Jiangsu province, while infections have spread to at least four other provinces.

It is geographically the largest spread for several months, challenging China's aggressive containment efforts which have relied on mass testing, lockdowns and swift contact tracing.

The virus first emerged in the central city of Wuhan, but China has extolled its success in largely extinguishing the pandemic inside its borders, allowing the economy to rebound.

The new outbreak, coupled with cases seeping over the porous border with Myanmar, is threatening that record.

Officials in Jiangsu have locked down hundreds of thousands of residents, Lu Jing, a member of the epidemic prevention taskforce, told reporters Thursday.

"Internet cafes, gyms, cinemas and karaoke bars and even libraries in Nanjing have been shut down," he said.

The city has tested all 9.2 million residents twice, he said, adding that the highly contagious Delta variant is posing challenges to containment efforts.

The southwestern province of Sichuan reported three new cases Thursday while Beijing reported two locally transmitted infections, the first in six months.

The high-end Legendale Hotel Beijing was locked down after a reportedly imported virus case among guests
The high-end Legendale Hotel Beijing was locked down after a reportedly imported virus case among guests AFP / Noel Celis

The Beijing patients -- a married couple -- living on the outskirts of the Chinese capital, tested positive after returning from a tourist hotspot in central China, a health official said.

More than 650 close contacts have since been identified and quarantines imposed.

"It is currently the summer vacation, a peak period of tourism, travel and gatherings... There should be no slack in prevention and control of the epidemic," Pang Xinghuo, deputy director of the city's centre for disease control, told reporters.

A high-end hotel in downtown Beijing has been locked down after media reported an imported case was found among the guests.

Police and workers wearing PPE suits were seen outside the Legendale Hotel on Thursday.

Most of the patients testing positive in the latest outbreak have already been vaccinated, raising concerns about the efficacy of vaccines against new variants.

China is racing to vaccinate at least 65 percent of its 1.4-billion population by the end of the year.

The country had administered 1.6 billion doses of the vaccine as of Wednesday, the National Health Commission said, without offering details on the number of people fully inoculated.