The plane, which had been expected at the Aviodrome, "crashed in South Africa during take-off on a test flight", it said.
Police spokesman Isaac Mahamba told South African broadcaster eCNA: "There is smoke all over and paramedics are on the scene".
"Initial reports from the aircraft crash in Wonderboom [say it] has left allegedly 20 people injured, at least one critically", ER24 tweeted.
Photos on social media showed the plane's fuselage broken, dented, and charred.
One fatality has been confirmed.
Rudi Storm, who claims to have witnessed the incident, says they noticed the right-hand-side engine was on fire and the plane was flying very low.
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Eyewitnesses described seeing the plane attempt to veer toward Wonderboom airport, then hearing an explosion.
"There are critical patients‚" Loubser said.
The plane had been due to fly later this week to Aviodrome via east Africa, through Egypt, Croatia, Austria to the Netherlands.
The plane was marked Martin's Air Charter.
A charter aircraft crashed in Kameeldrift on Tuesday afternoon.
South African Civil Aviation Authority spokesman Kabelo Ledwaba said its investigators were at the scene and would issue a statement.