Papua New Guinea's volatile Ulawun volcano - known as one of the world's most hazardous - erupted on Wednesday, spewing lava high in the air and sending residents fleeing.
A pilot for Niugini Helicopters flying near the crater witnessed a column of lava spurting vertically into the equatorial sky, along with ash that has been belching since early morning.
Ulawun, on the remote Bismarck Archipelago chain, is listed as one of 16 "Decade Volcanoes" targeted for research because they pose a significant risk of large, violent eruptions.
Witnesses said lava had cut off the main highway in the north of the island.
"The volcanic activity at Mt Ulawun began at 7:00 am this morning after slight rumbling and light emission," Leo Porikura, an official with the West New Britain Disaster Office, told AFP earlier.
"The Rabaul Volcano Observatory has declared a stage one alert warning of a possible eruption."
Witnesses had reported ash spewing out of the 2334-metre summit, sending trails spanning high overhead.
"The sky has turned black," said Kingsly Quou, manager of the nearby Mavo Estates palm plantation.
Mr Quou said that villagers living at the base of the volcano had already been evacuated and he and his colleagues were gathering their belongings.
Japanese satellite imagery and sources on the ground had shown sulphur dioxide and now volcanic ash drifting from the crater.
Australia's Bureau of Meteorology said the ash reached more than 13km into the air.
The bureau's Darwin Volcanic Ash Advisory Centre issued a "red" warning to airlines, indicating the eruption was imminent, although there is not believed to be an immediate threat for flight routes.
Thousands of people live in the shadow of Ulawun, despite it being one of the most active volcanoes in the country.
Mr Porikura said people living in the vicinity of the volcano had been instructed to move away to safer areas and a disaster team had been dispatched.
"The disaster team will liaise with the local community, local businesses and local level government authorities to prepare for a possible eruption," he said.
"Three crucial priority areas being addressed include transport plan, care centre preparations and getting the communities in the high-risk areas to prepare for an evacuation."
The nearby Rabaul Volcano Observatory said emissions from the volcano were getting darker, indicating a higher ash content - which can cause breathing problems, eye irritation and skin irritation because of the high acid content.
A team of experts had visited earlier this month and reported the volcano was "quiet" adding "there is no indication of any change in its state of unrest."
The ash emissions had been proceeded by an increase in seismic activity, Mr Porikura said.
