Missionaries and at least one child were among the 13 people on board travelling to Ferguson Island off PNG’s south-east coast.
Anton Salavyov of the International Missionary Society Seventh-Day Adventist Church Reform Movement said two of the church’s pastors were among those threatened.
He said it was a miracle the group survived.
“Some of the people including the captain of the boat jumped in the water to swim.
“And actually there was everything taken from them – but after the pirates had gone they looked around and found a small mobile phone they missed stealing and they managed to call people for help.”
Pastor Anton said it was the first such experience for his church, which did missionary work in several Pacific countries.
“Of course we expect some danger. Always we are going under risk but until now we really have had no problem.
“This is a good lesson for us as well,” he said.
One of the missionaries described the attack as a slick operation run by a network of people.
Fijian Sanaila Ravia Kenivale was among the 13 people held up by about 10 pirates armed with guns and knives travelling in a seven-metre fibreglass boat.
Kenivale said locals told him later such attacks happened regularly and they were lucky to survive.
“Everything happened so fast. They jumped onto our boat. There was actually a machine gun pointing at us and the rest of the crew held bush knives.
“They jumped onto our boat and ordered everyone on the boat to go overboard,” he said.
Kenivale said he thought they were not killed because they had a child with them.
The boat passengers managed to get back on board the boat after the gang abandoned them.
They made a phone call with a mobile phone and were picked up after floating with no engine for about three hours.
Kenivale said locals later told them they only travelled on high-powered speed boats to avoid being attacked as it was such a regular occurrence.
He said he was told people were normally left to be eaten by sharks.
Kenivale said he had been in touch with the Fiji High Commission in Port Moresby about the attack.
He said the PNG police had apologised but said they did not have enough resources to pursuethose responsible.
Kenivale suspected his group was followed from the town of Alotau from where they set out.
He said there appeared to be a network of people involved.
In recent years the authorities have struggled with piracy in the New Guinea Islands region.
There have also been instances of piracy involving small boats travelling to and from Alotau in the south.
Five scientists and three crew were believed to be abducted by pirates while travelling to an island off West New Britain in 2011. Their boat was found floating off the East Sepik coast months later, but the group remains missing. - RNZ