A group of 33 worshippers gathered for a baptism ritual were swept away by a flash flood on the Jukskei river on Saturday, South African emergency services reported.
At least nine people have died in a flash flood in the Johannesburg metropolitan area, which was hit by heavy thunderstorms on Saturday.
Rescue efforts are continuing to find others after a break overnight, with at least 15 believed to have been initially swept away, emergency services said on Sunday.
"A group of people were taking part in religious rituals in the river last night when a storm hit," said Robert Mulaudzi, Spokesperson of the City of Johannesburg Emergency Management Services.
Mulaudzi added that there were 33 worshippers on the banks of the small Jukskei river at the time of the dramatic flooding. One person has been rescued.
Local media are reporting that the group was taking part in a baptism ritual.
"Maybe the message to our residents out there is to be cautious as and when they conduct these kind of rituals to make sure they exercise caution, they do it in a safe place, and ensure that the safety measures are considered so that we can be able to prevent incidents like these," Mulaudzi said.
Although shallow, the Jukskei river is known to have caused floods before, with hundreds of makeshift homes swept away in the township of Alexandria in November 2016.