Around 2000 of the island’s 9000 population had to be evacuated to safer ground in the early hours of Saturday.
The natural disaster began at 6am local time, sending an ash column more than 15km above sea level, the Rabaul Volcano Observatory (RVO) said.
The ash falls were so dense that sunlight was blocked for hours and trees broke under the weight.
"The most affected areas are Baliau and Kuluguma and due to the very poor visibility caused by the ash fall, people are using torch light to move around," the RVO’s information bulletin read.
The observatory’s principal geodetic surveyor, Steve Saunders, said that although the initial phase of the eruption was over, a new vent opening indicated that further volcanic activities were expected.
"There are no casualties as far as we know but we are telling people to keep away from valleys for risk of mud flows ... there's a heavy thick blanket of ash on the flank and if there is heavy rainfall, we are making people aware of the threat," he said by phone.
Located on the north coast of Papua New Guinea, Manam Island is just 10km wide and is home to the Pacific nation's most active volcanoes.
Local journalist Scott Waide shared footage and photos online of lava and ash emitting from the volcano.
In December 2006, another major eruption killed more than a dozen residents. They were killed after breathing in the ash or being buried by landslides.
Additional reporting by Reuters
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