Gunmen in southern Nigeria have killed a local driver and kidnapped as many as seven people, at least three of whom are Australian citizens and one an Australian resident, Prime Minister Malcolm Turnbull said on Thursday.

There was some initial confusion over the number of victims and nationalities of those involved, as police in Nigeria gave conflicting accounts.

The workers, two of whom police said later escaped, were contractors for cement company Lafarge Africa. They were attacked on the outskirts of the city of Calabar at around 05:30 a.m. (local time), police said.

Calabar is a coastal city 570 kms east of Lagos, and the capital of Cross River State in the Niger Delta region, where both criminal gangs and militants have been active.

Prime Minister Malcolm Turnbull called the incident a “very serious kidnapping” in response to a journalist’s question and urged calm in reporting the incident.

“These are the facts as we know them: three Australians and one Australian resident were among seven people kidnapped in an attack on an Australia contractor’s operations in Nigeria. One person was killed in the attack,” Mr Turnbull told reporters.

Two expatriates managed to flee, said Irene Ugbo, a spokeswoman for Cross River state police, adding that she did not know the nationality of any of the workers feared still held.

Ugbo had earlier said that only two of the kidnapped were Australians, and one was a New Zealander, while another police officer said a South African had been abducted.

The kidnappers had not contacted police, she said.

Meanwhile, Foreign Minister Julie Bishop said the government is working closely with Nigerian authorities.

“The government is in close contact with the Nigerian government, which is taking the matter extremely seriously,” she told reporters.

Kidnappings of foreigners are common in the Delta region, which holds most of the crude oil whose sales make about 70 percent of Nigeria’s national income.

OPEC member Nigeria was Africa’s top oil producer until a recent spate of attacks on oil facilities pushed it behind Angola. Production has fallen from 2.2 million barrels at the start of the year to around 1.6 million barrels, helping push up global oil prices.

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

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

Macmahon Holdings Ltd, which was placed on a trading halt in the wake of the incident, could not immediately be reached for comment.

– with Reuters