The plight of around 1,500 villagers, left without a protein source and livelihoods by the suspected water poisoning, was brought to the attention of the Pacific nation's leaders by ocean campaigners, who have urged a faster government response.

John Aini, who runs a local ocean protection group, Ailan Awareness, started hearing reports of fish dying across New Ireland province in December.

Visiting five villages there, he observed a red tide lurching in from the ocean.

"I was there when fish were gasping for air," he told AFP.

Over five days, the group recorded 3,451 dead marine creatures, including fish with discoloured and bulging eyes and green flesh, and a sulphuric smell near reefs.

At least 750 people reported illness such as chest pains, skin ailments and coughing after eating fish and wading in the sea.

Papua New Guinea's fisheries minister Jelta Wong said that New Ireland residents should stop eating fish as investigators test for contaminants, including chemicals used in industrial activity along the coast.

"We don't know which chemical is in the fish," he told parliament on Wednesday.

The investigation would take "a week or two" to identify a health response, he said.

"Our people are kept in suspense about what is affecting the fish," Aini said on Thursday.

"They have gone back out to sea to go fishing because where else will they get food from? They are taking risks," he said.

The fishers had mistakenly hoped that new schools of fish arriving to the coast would avoid the same fate, he said.

Bodhi Patil, the founder of Innerlight Foundation, which helps indigenous communities protect the ocean, also visited the villages.

He said he spoke to a boy unable to afford school fees because his family had lost its primary income source from fishing.

There is also concern that children are not eating enough protein.

"It creates a big problem telling people not to eat fish when they don't have any other food sources besides local greens and fruits," he told AFP.

"These villages are extremely poor."

The ocean groups are raising money online, and plan to take water tanks and medical supplies to communities next week.