Prime Minister Malcolm Turnbull has confirmed that three Australian citizens and one resident are among a group of people kidnapped in a fatal ambush on their vehicle in south-east Nigeria.

The driver of the vehicle was shot dead in the attack on the outskirts of the city of Calabar, the capital of Cross River State, about 5.30am on Wednesday, local time, Nigerian police commissioner Jimoh Ozi-Obeh said.

Five people who worked for Australian mining and engineering giant Macmahon, which was contracted to cement company Lafarge Africa, were abducted, Nigerian police said.

Peter Zoutenbier, from Brisbane, was one of those kidnapped, his family have said. 

There have been reports all the workers were based in Perth and that at least one was from Western Australia.

Mr Turnbull said on Thursday he believed seven people were kidnapped, including three Australian citizens and one Australian resident. One person was killed in the attack and the incident was "very serious".

Mr Turnbull said the Australian high commissioner was on the scene and officials were working with local authorities "at the highest levels".

"We don't know at this stage the identity of the kidnappers and the families in Australia have been notified," he said.

Mr Turnbull encouraged the media "to be restrained in your reporting. In many respects the less Julie [Bishop] and I say about this the better from the point of view of recovering the kidnapped people".

Earlier, Ms Bishop said the Australian government was working to confirm details of the reported kidnapping in Nigeria of four Australians, who had been working for an Australian mining company.
 
"The Australian government is in close contact with the Nigerian government, which is taking the matter extremely seriously," she said.

About 30 militants ambushed the vehicle near the Idundun Bridge crossing over a river, local media reported. 

After the attack, the kidnappers fled with the hostages aboard a boat that was hidden under the bridge.

A witness told local media organisation Vanguard that those kidnapped were travelling in a convoy of four vehicles when the militants opened fire on them.

"They ambushed them and killed [the driver] on the spot. One of the expatriates hid under the vehicle and they didn't see him because it was still a bit dark," the unnamed witness said.

"They also took one of the drivers ... then one supervisor and three white guys and it was like they had a boat by the beach already waiting for them."

Mr Ozi-Obeh initially reported that two Australians, one South African and two Nigerians were kidnapped, while the driver of one of the vehicles was shot dead. 

Another report said a New Zealander, rather than a South African national, was among those kidnapped. 

Two of those kidnapped managed to flee, said Irene Ugbo, a spokeswoman for Cross River State police. She did not know the nationality of the workers still being held.

The kidnappers were yet to contact police, she said.

Lafarge Africa said it had been informed of the incident by Macmahon.

"Macmahon is working with the security agencies to resolve this situation," said Viola Graham-Douglas, a spokeswoman for Lafarge Africa.

Macmahon could not immediately be reached for comment.

According to its website, Macmahon has a seven-year contract for quarrying operations at United Cement Company of Nigeria Ltd's cement manufacturing plant in Mfamosing, near Calabar.

"Macmahon undertakes a range of works at the site including overburden removal and the drilling, blasting, excavation and delivery of limestone, marl and shale from the quarry to the cement plant crushers," the company's website says.

Macmahon has put its shares in a trading halt ahead of an announcement relating to the kidnapping of the contract workers.

With Nathanael Cooper

 

- with Reuters