The information was announced at a meeting on Thursday as the city detected a new Covid-19 cluster started from a religious mission in Go Vap District the previous night.
The areas involved in the cluster are Districts 1, 3, 4, 5, 10, 12, Binh Chanh, Binh Thanh, Binh Tan, Go Vap, Hoc Mon, Nha Be, Phu Nhuan, Tan Binh, Tan Phu and Thu Duc City.
Until now, at least 25 people linked to the Revival Ekklesia Mission, including a chef at five-star Sheraton Saigon Hotel, have tested positive for the coronavirus.
Among them, 19 are members of the mission and six others have had contact with the infected members.
The cluster was detected after three members sought health checks with respiratory conditions at Gia Dinh Hospital in Binh Thanh District on Wednesday and tested positive.
By Thursday noon, 403 people have been identified as direct and indirect contacts of the infected. Among the 67 direct contacts, 23 have tested negative for the virus while the other results are not yet available.
Among the indirect contact, 326 have tested negative and 10 still await results.
"The infection level of this group is high," said Nguyen Tan Binh, director of HCMC's Department of Health.
Binh admitted that there was loophole in the city's pandemic prevention work and task forces have failed to detect the cluster earlier.
"It is possible that infection had spread around before the first three members were found positive on Wednesday night, and that the source of transmission had already existed in the community," he said.
Members of the mission, which describes itself as a Christian congregation and a non-denominational, evangelical, charismatic church, usually gather in a small house in a narrow alley in Go Vap District and almost all have tested positive.
Initial investigation found 22 members gathered several times in the alley house this month.
It has been confirmed that the mission has 24 official members but the actual figure of members could be higher because many families have joined it but just one family member registered.