At least 29 passengers aboard a train that started from Lhasa in Tibet autonomous region on Monday and arrived in Beijing on Wednesday tested positive for COVID-19 after they disembarked at different stations.

The train, Z22, had 10 stops along its 40-hour journey, passing through several provinces, Beijing Daily reported.

As of Friday, Beijing and four provinces had reported a total of 29 positive cases - 2 in the capital, 13 in Hebei, 5 in Henan, 7 in Shanxi, 1 in Shandong and 1 in Gansu. All tested positive after they got off the train, according to local authorities on COVID-19 prevention and control.

Among them, Beijing's Shunyi and Daxing districts reported two asymptomatic carriers on Thursday. The one in Shunyi got off the Z22 train at Hebei's capital city Shijiazhuang and transferred to Handan in Hebei, then to Beijing on Wednesday.

Hebei reported 2 asymptomatic carriers on Wednesday and 11 asymptomatic carriers on Thursday - 8 in Cangzhou, 3 in Shijiazhuang, 1 in Hengshui and 1 in Handan. They got off at Shijiazhuang North Railway Station on Wednesday.

To curb further transmission, some districts in Shijiazhuang have started universal nucleic acid testing, including the districts of Chang'an, Qiaoxi and Xinhua. Residents of the places need to do the tests for three consecutive days.