"I can see an ash plume coming out," Ima Itikarai, head of the Rabaul Volcanological Observatory, told Reuters last week.

"There has been no lava, but the explosions have thrown rocks up to 700 metres (2,300 feet) from the summit," Itikarai said.

"There has been a reduction in pattern and emissions since Sunday. There is no need for evacuations," he said.

Itikarai said light ash had fallen on Rabaul, a port town on New Britain island 800 km (500 miles) northeast of the capital Port Moresby.

Air Nuigini stopped flights to Rabaul on Wednesday.

"Volcanic ash is within the vicinity of the aerodrome and we can't get in. We have suspended flights indefinitely," said an Air Nuigini official.

Rabaul, the provincial capital of New Britain, was devastated in 1994 when two volcanoes on either side of the town erupted, forcing the evacuation of 30,000 residents.

Five people died in the 1994 eruptions.

Another volcano on the southern end of New Britain island continues a low-level, two-month eruption, causing lava flows around its caldera, said the Rabaul volcanologist.

Toxic ash has rained down on farmland around the Mount Pago volcano making the area uninhabitable and affecting up to 15,000 people.

Mount Pago, about 50 km (30 miles) south of the town of Kimbe, began erupting on August 5. Mount Pago, a relatively unstudied volcano, last spewed smoke and ash in 1933 and erupted in the 1920s.