One person died and 20 others - 18 passengers and 2 factory workers - were found injured after a charter plane crashed into a Kameeldrift factory. Picture: Oupa Mokoena/African News Agency (ANA)

Johannesburg - The death toll from a plane crash near Pretoria, South Africa rose to two on Wednesday, the plane's owners confirmed.

Television station eNCA reported the 1954 plane belonged to the Dutch National Aviation Museum, Aviodrome, and was undertaking a test flight before being moved to the museum.

The plane crashed into a factory near Wonderboom airport on Tuesday, with one initially confirmed dead and 20 others injured.

"Unfortunately, it has just been confirmed that a second person has been killed, one of the factory workers," Aviodrome tweeted Wednesday. 

"Our thoughts and our sympathy go out to the surviving relatives."

It is not yet clear what caused the plane to crash but South Africa's Civil Aviation Authority is investigating.