Papua New Guinea's volatile Ulawun volcano -- designated one of the world's most hazardous -- began spewing ash Wednesday, turning the sky dark, sending residents fleeing and prompting an eruption warning.
The volcano 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.
"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.
"The Rabaul Volcano Observatory has declared a stage one alert warning of a possible eruption."
Witnesses reported ash spewing out of the 2,334 metre (7,657 foot) summit, sending trails spanning high overhead.
"The sky has turned black," said Kingsly Quou, manager of the nearby Mavo Estates palm plantation.
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 13 kilometres (44,000 feet) into the air.
The bureau's Darwin Volcanic Ash Advisory Centre issued a "red" warning to airlines, indicating the eruption was imminent or underway, although there is not believed to be an immediate disturbance for flight routes.
Thousands of people live in the shadow of Ulawun, despite it being one of the most active volcanoes in the country.
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," Porikura said.
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 ans 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, Porikura said.