Spokesman for the Metsimaholo municipality, Gino Alberts, said he could not verify how the woman was killed.

Heavy rains struck Amelia township around 9pm on Tuesday.

"Around 1000 households were affected, but the exact figure of how many people were affected is still not clear," he said.

The injuries ranged from minor to serious. Alberts said disaster management teams were assessing the situation.

"We are doing everything in our power to assist the affected families and we are appealing to people to help with food or blankets... They can deliver these things at the safety department in Sasolburg."

The SA Weather Bureau said the Free State could expect more rain throughout the day. There was a 60 percent chance of showers and thundershowers in the afternoon, forecaster Khushulwa Msimanga said.

"A severe thunderstorm has started to develop in the southern and central parts of the province and this is expected to continue into the evening," he said.