There is a plot to kill two State witnesses who testified against three taxi bosses accused of multiple murders in a taxi war in Mpumalanga and Gauteng in the 1990s, authorities said on Wednesday.

"I can confirm that our relevant operational managers in Mpumalanga are aware of the potential threat and are managing the situation," said correctional services department spokesman Koos Gerber.

"Obviously we cannot elaborate more on any special measures or arrangements."