Six people died when a bridge on the R65 between Ermelo and Lothair collapsed in heavy rain, the Mpumalanga department of community safety said.
Spokesman Joseph Mabuza said three vehicles, one of them a taxi, crashed into the broken bridge.
Six people died and five were seriously injured. Mabuza said several others were missing.
The bridge was swept away just before 9pm.
He said motorists should use the R33, N17 and the Ermelo/Mpuluzi road as alternative routes because the R65 remained closed in the vicinity of the accident.
