Auditing firm Deloitte was reeling with the news that four of its employees were among six people killed in a plane crash in Germiston on Tuesday.

"We are all in shock and devastated at this news. We are currently focusing on providing support to the families of the victims as well as their colleagues at Deloitte," said chief executive officer Allen Swiegers in a statement.

"They were part of a close-knit Deloitte family and will be greatly missed."

Audit partners Mahen Naidoo (43), and Lesley Philpott (28), accountant in charge Mark Kriel (25), and audit trainee Gillian Brown (23), were on their way to Lesotho with Michelle Rose-Martin and Peter Woodstock, both employees of Circuit Breaker Industries, a division of electrical engineering company Reunert. The plane came down near Germiston's Wesbank Raceway.

Brown was the daughter of audit partner Allan Brown.

"We express our deepest condolences to Allan and the parents, spouses, fiance, families and friends of all who died," the company said.

"We have been in touch with the managing director of CBI and expressed our condolences to CBI and Reunert."

Mysterious circumstances

Their light aircraft took off at 8.10am and about 2km into its journey to Ficksburg in the eastern Free State the pilot called in to request an emergency landing, said airport manager Anton Kruger.

However, the aircraft broke up and burst into flames as it came down near the busy N3 highway.

In August one person died and two were injured when their light aircraft crashed into a stream near the golf course, which is opposite the airport.

Police were expected to release the names of the other victims later.