Four suspected pirates have been killed in a gunfight involving the Danish navy in the Gulf of Guinea in an incident that marks a real shift in the battle against the criminal gangs.

Shipowners' organisation Danish Shipping and the Danish navy said the battle took place in waters south of Nigeria on Wednesday night.

The incident illustrates how dangerous the area is and how critical the presence of the Danish frigate Esbern Snare is, Danish Shipping said.

It is also the first time pirates have been killed by an international naval vessel off West Africa.

The warship had sailed to the region from Denmark at the end of October.

Quickly into action

On Wednesday night, the frigate was responding to reports of increased piracy risks off Nigeria.

"After having observed a suspicious motorboat with eight men on board, the Frogman Corps was sent off in a high-speed amphibious rigid inflatable boat [RHIB]," Danish Shipping said.

The naval personnel fired warning shots but were subsequently shot at, prompting the Danish team to engage in a shootout, which resulted in the deaths of four pirates. Another man was injured.

"I am deeply grateful that the pirates were apprehended in time, and that our deployed soldiers with Esbern Snare performed their duty of safeguarding the crew on board our vessels," Danish Shipping chief executive Anne Steffensen said.

Steffensen is currently in Ghana with Danish Prime Minister Mette Fredriksen to visit the officers on board the Esbern Snare.

"We have always said that the Gulf of Guinea is the world's most dangerous water, and the situation of last night stresses the seriousness of the situation here," Steffensen said.

"There is definitely a need for the presence of the Danish soldiers, and even though it may sound tough: piracy comes with a price."

Piracy equipment spotted on skiff

Anne Steffensen, chief executive of Danish Shipping, praised the navy's actions. Photo: Danish Shipping

The Danish navy said the frigate had sent a Seahawk helicopter in advance to observe the area.

The crew of the helicopter found a speeding motorboat in an area with a number of merchant ships.

A number of the tools associated with piracy were spotted on the skiff, including ladders.

The navy added that Esbern Snare called the suspected pirates to bring them to a halt so that Danish soldiers could get on board.

When the men did not react, the Danish forces fired the warning shots.

The criminal suspects then opened fire directly at them.

No Danish soldiers were injured, but the pirate boat sank after the incident.

Pirates arrested

A number of other gunmen were taken on board the frigate.

Maritime security company Dryad Global said the incident represents a "key milestone in the evolution of piracy within the Gulf of Guinea".

"Whilst a logical consequence of naval forces being deployed to protect commercial shipping against the threat of hijack and kidnap, this is the first time where suspected pirates have been killed by an international naval vessel operating within the region," the company said.

Dryad described the Danish navy as a highly trained and formidable maritime force that was acting in self-defence.

But the company warned: "Pirates continuing to target commercial vessels operating within the Gulf of Guinea are unlikely to be significantly deterred from conducting such operations in future."

However, the firefight shows the Danish government's intent to have an enforcement impact in the region under its sovereign mandate, Dryad believes.

The wider question is whether a multinational coalition could help nations shoulder the burden and not leave it to individual navies, the company said.

The Esbern Snare will spend around six months in the region. There are about 175 personnel on board.