At least nine people have died in South Africa after they drowned during a flash flood along the Jukskei River in Johannesburg, emergency services said on Sunday.

They were swept away during a baptism ceremony, officials said. It is believed another eight people are still missing.

“We recovered two bodies yesterday and another seven today,” Robert Mulaudzi, Johannesburg Emergency Services spokesman, told DPA news agency.

The number is expected to rise as the search-and-rescue operation continues.

Mulaudzi said that 33 worshippers had gathered along the banks of the river in the Johannesburg suburb of Bramley Park for the baptism ritual on Saturday, December 3. A sudden storm caused the flash flood and a strong current, he said.

Congregations often gather to conduct church rituals including cleansing and baptism along the Jukskei River, which runs along many townships including Alexandra in the east of Johannesburg.

In June, four people drowned at baptism ceremonies in the country’s Limpopo province, and over Easter this year the Water and Sanitation Department sent out a special warning against holding baptism ceremonies in rivers.

Mulaudzi asked churches that carry out such ceremonies to be more aware of storms and flash floods that are common at this time of year.