"Initial reports from the aircraft crash in Wonderboom [say it] has left allegedly 20 people injured, at least one critically", ER24 tweeted.
Emergency services were called out to the scene just after 16:00 when the plane was found on fire in a field.
The 1954-built plane was soon to be flown to the Aviodrome air museum, near the central Dutch city of Lelystad, via Egypt, Croatia and Austria.
"Medics from ER24 and other services are at the scene of a plane crash at Wonderboom in Pretoria", said Russell Meiring, spokesman for the ER24 medical service.
Meiring said there were two air ambulance helicopters on the scene.
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Eyewitnesses described seeing the plane attempt to veer toward Wonderboom airport, then hearing an explosion.
Police spokesman Isaac Mahamba told South African broadcaster eCNA: "There is smoke all over and paramedics are on the scene".
Details of the cause of the crash on Tuesday are yet to be established, but authorities confirmed that the plane hit a factory building before crashing. "Martin's Air Charter" is written on the side of the fuselage.
"They are busy treating one of the pilots. and he will be airlifted to a Netcare hospital", he said.
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