Three Chinese workers kidnapped by gunmen in central Nigeria's Kogi state were released unhurt on Saturday, police said.

"I can confirm to you that the abducted Chinese workers have been released. They were freed today through a joint operation by the police and other security agents," state police spokesman Sola Collins Adebayo told AFP.

He said the hostages who were seized on Friday at a quarry outside state capital Lokoja were unharmed, but declined to say if a ransom was paid.

A senior police officer told AFP earlier on Saturday that the gunmen had stormed the quarry and engaged the police on guard there in a shootout that left one officer dead and another wounded.

The assailants then escaped with their hostages on foot through the bush, with the police on their trail.

Kogi state has seen a wave of abductions targeting foreigners this year.

Two weeks ago, two other Chinese nationals were kidnapped in the state, while an American missionary was taken from her school last month.

The missionary, who works in the village of Emiworo where her Free Methodist Church runs a community organisation, was released last week.

State police said they were unaware of any ransom paid for her release.

Foreign nationals have often been kidnapped in Nigeria by local gangs who typically release hostages following a ransom payment.

Policeman killed as gunmen abduct three Chinese in Nigeria
Lagos (AFP) March 14, 2015 - Gunmen abducted three Chinese workers after a shootout that left a police officer dead in central Nigeria, police said Saturday.

"Three Chinese nationals were abducted by some unknown gunmen within the early hours of Friday," a senior police officer told AFP, requesting anonymity.

He said the gunmen had stormed a quarry outside Lokoja, the capital of Kogi state, and engaged the policemen on guard in a shootout.

"One policeman was killed while another sustained gunshot wounds," he said.

He said the assailants escaped with their hostages on foot through the bush, adding that police were on their trail.

It was unknown whether the kidnappers were planning to demand a ransom.

Kogi state has seen a wave of abductions targeting foreigners this year.

Two weeks ago, two other Chinese nationals were kidnapped in the state, while an American missionary was taken from her school last month.

The missionary, who works in the village of Emiworo where her Free Methodist Church runs a community organisation, was released last week.

State police said they were unaware of any ransom paid for her liberation.

Foreign nationals have often been kidnapped in Nigeria by local gangs who typically release hostages following a ransom payment.

Such abductions are especially common in the southern, oil-producing Niger Delta, where expatriates working with large oil companies have been a frequent target.

A number of foreigners have also been kidnapped in the north of the country, but those attacks claimed by Boko Haram or the linked Islamist group Ansaru are considered a different phenomenon, and not necessarily motivated by a desire for ransom.

A number of people seized by Nigerian Islamists have been killed by their captors, while others have died during botched rescue operations.