London, Apr. 10: An "explosive" volcanic eruption has blanketed the Caribbean island of St Vincent in ash and smoke and forced thousands of people out of their homes.

La Soufrière, which has been dormant for decades, first started showing volcanic activity in December, but that increased this week.

On Thursday, Prime Minister Ralph Gonsalves urged more than 16,000 residents in "red zones" to evacuate. The volcano has since spewed dark ash plumes 6 km (3.7 miles) into the air.

Ashfall has been recorded as far from the volcano as Argyle International Airport some 20 km away, St Vincent's National Emergency Management Organisation (Nemo) said.

The volcano had been dormant since 1979, but in December it started spewing steam and smoke and making rumbling noises.

The first sign that an eruption was imminent came on Thursday evening when a lava dome became visible on La Soufrière.

That same night, Mr Gonsalves ordered an urgent evacuation of the surrounding area.

Then just before 09:00 on Friday (13:00 GMT), seismologists from the University of the West Indies confirmed that an "explosive eruption" was underway.

Evacuees were taken to cruise ships and safer parts of the island.

One resident, Zen Punnett, told AFP news agency that he saw "a huge ball of smoke", and that there was panic when people were first ordered to evacuate.

"I can feel and hear rumbling here in the green safe zone... keeping calm as much as possible and praying," he added.

Lavern King, a volunteer at shelters on the island, told Reuters news agency: "People are still being evacuated from the red zone, it started yesterday evening and into last night. The place, in general, is in a frenzy."

Later on Friday, another explosion was recorded, the UWI Seismic Research Centre tweeted.

Some evacuation procedures were hindered by the heavy ashfall, which had made visibility "extremely poor", Nemo said.

"Now that the La Soufrière volcano has begun erupting explosively, ash falls will soon overwhelm us," the organisation wrote on Facebook, adding: "Be sure to get rid of or clean up the ash, soon after it falls. If rain falls, the ash could harden and pose a danger to you."

Most of the Lesser Antilles islands are part of a long volcanic arc in the Eastern Caribbean.

The last eruption, in 1979, caused more than $100m (£73m) of damage on the island.

The worst eruption on record, in 1902, killed more than 1,000 people.

Local media have also reported increased activity from Mount Pelee on the island of Martinique, north of St Vincent.