Three Australians, two Nigerians, a New Zealander and a South African have been kidnapped in Nigeria in an ambush that killed their Nigerian driver, Australian officials said Thursday.

Authorities did not know who kidnapped the men, who were working for Australian mining contractor Macmahon Holdings, on Wednesday, Prime Minister Malcolm Turnbull said. Macmahon has declined to comment.

Turnbull said the Australian ambassador was on the scene and working with local authorities.

Another Australian had escaped during the ambush at Cross River Province, Foreign Minister Julie Bishop said.

"We are treating this extremely seriously as, I understand, is the Nigerian government," Bishop told reporters.

"We have some understanding of what occurred," she said. "Suffice to say there are seven people currently being held."