The Chinese mainland has detected its first two COVID-19 cases of the Omicron variant in the northern port city of Tianjin and the southern coastal province of Guangdong this week, as health officials and experts said China's virus monitoring system and disease control policies are capable of timely detection of the virus and cutting its transmission.

The patient in Guangdong was confirmed to be a 67-year-old man in the provincial capital of Guangzhou, local authorities said during a briefing on Tuesday.

He flew to China from overseas on Nov 27 and tested negative for the novel coronavirus multiple times during centralized isolation in another city. On Dec 11, he finished the quarantine and flew to Guangzhou for self-isolation at home.

The patient tested positive for the virus on Monday and was diagnosed as having mild symptoms. Genome sequencing results later revealed that he was infected with the Omicron variant.

Chen Bin, deputy head of the city's health commission, said that as of Tuesday noon, all people related to the case had tested negative for the virus.

The patient is the second Omicron case discovered on the mainland.

The first infection with the new strain was reported on Monday involving a traveler who arrived in Tianjin from a European country on Dec 9. The patient was also confirmed as contracting the Omicron variant based on genome sequencing results, said local authorities.

Gu Qing, director of the Tianjin Health Commission, said the patient is asymptomatic.

"A special team of doctors has been arranged for the patient, who is now receiving treatment at a designated zone at the Haihe Hospital," Gu said on Tuesday.

The hospital has also increased the use of traditional Chinese medicine therapies for the patient, according to the commission.

Gu added that no other infection had been found among passengers on the same flight and "closed-loop management is provided for them".

"Heightened attention will be devoted to monitoring the health condition of each of them and tracking their nucleic acid testing results," he said. "We will also intensify supervision and sanitization of quarantine facilities, as well as the places and people they come into contact with."

The Omicron variant is highly concerning due to a large number of mutations associated with higher transmissibility and its potential to thwart immune responses. Since it was first reported in South Africa in November, human infections with this variant have been identified in more than 60 countries, according to the World Health Organization.

Wu Hao, a disease control expert of the State Council's Joint Prevention and Control Mechanism, said on Tuesday that the mainland's first Omicron case－in Tianjin－was promptly discovered at a quarantine site for incoming travelers from overseas, which attests to the sensitivity of China's disease monitoring system.

"Even if the new strain begins spreading locally, we can eliminate it and reduce its impact on normal life and production with the implementation of current virus control policies," he said in an interview with Beijing Daily.

He added that it is essential for the public to strictly abide by personal protective measures, such as wearing masks and washing hands regularly, as well as adhering to isolation requirements based on their individual travel history.

The new strain of the virus has also put port cities on alert, which are at higher risk of local transmission of the virus, Wu said, adding that local authorities in such areas should set up a task force to coordinate virus control work, intensify management of at-risk staff and establish buffer zones to minimize its impact on society.

Gu, the health official in Tianjin, said the city has increased the frequency of testing for at-risk and key workers. As of Monday, the city had fully vaccinated nearly 94 percent of its residents over age 12, he said.

China reported 51 domestic confirmed infections on Monday, down from 80 on Sunday, according to the National Health Commission.

Recent local outbreaks have been concentrated in Zhejiang province, the Inner Mongolia autonomous region and Heilongjiang province.

Ma Zhenhuan in Hangzhou contributed to this story.