La Soufriere volcano on the Caribbean island of St Vincent "explosively" erupted this morning, spreading ash across surrounding villages and forcing thousands to flee to safety.

In a press conference today, journalists were told that the eruption was "likely to continue for days and possibly weeks".

This morning's blast sent plumes of hot ash and smoke 6,000 metres into the air, the local emergency management agency said. 

Video posted on the website showed a tower of ash being belched out and expanding roughly into a ball shape as it rose upwards. No deaths or injuries have been reported.

"Please leave the red zone immediately. La Soufriere has erupted. Ash fall recorded as far as Argyle International Airport," the National Emergency Management Organisation said.

The airport and volcano are at opposite ends of the 28km long island.

La Soufriere, the highest peak in Saint Vincent and the Grenadines, has been dormant for decades. Its largest blow-up happened over a century ago, killing more than 1,000 people in 1902.

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Prime Minister Ralph Gonsalves started issuing evacuation orders last night for residents in so-called red zones, home to some 16,000 people on the biggest island in the archipelago. The total population of the chain is about 100,000.

"Persons living in the 'Red Zones' are strongly advised to pack a quantity of personal items, secure your homes and animals; and be ready to be evacuated immediately," police said in a statement after the eruption.

Royal Caribbean International and Celebrity Cruises said in a press release they were sending two ships to assist the evacuation effort.

Mr Gonsalves said two more ships from cruise liner company Carnival were also on their way.

Those evacuated would be taken to shelters elsewhere in the island chain or other Caribbean territories that have offered assistance, such as Barbados and Saint Lucia, according to local media.

A US National Oceanic and Atmospheric Administration satellite image shows smoke coming from La Soufriere volcano on Saint Vincent and Grenadines

Philmore Mullin, director of Antigua & Barbuda's National Office of Disaster Services, told AFP the twin island nation was ready to receive evacuees from Saint Vincent.

He said between 12,000 and 15,000 people had already moved out of the red zones. "I know for sure they will be scared out of their wits. The question is, what will happen after they move? Volcanoes don't tell you what they are thinking," said Mr Mullin.

"If it continues to erupt for a long time it will be life-changing for them. And, depending on the type of eruption, they might not be able to get back home for years."