Experts said Monday's eruption, the largest since the volcanic activity began last week, was "destroying everything in its path" and posed a serious threat to residents yet to evacuate.
About 16,000 people were evacuated before eruptions began but an unknown number remained behind or refused to leave, according to the Associated Press.
St Vincent prime minister Ralph Gonsalves said on Saturday that empty cruise ships in the area were being rerouted to help the evacuation, but that people would need to be fully vaccinated to be accepted.
"The chief medical officer would be identifying the persons already vaccinated so that we can get them on the ship," Mr Gonsalves said.
He said the ships aren't fully staffed to keep evacuees on the ships, but that they can transport them to neighbouring islands if they are already vaccinated.
Those only recently vaccinated would have to wait "a day or two" after receiving the jab before being transported to other nations.
"If people are willing to welcome you at a time of Covid-19, they will wish you to have the highest level of protection possible," Mr Gonsalves said.
A spokeswoman for Celebrity Cruises told The Independent they will only require a negative PCR test for evacuees to board.
“Our ship remains off the coast of the island awaiting word on whether or not we will be needed,” she said.
Several companies that have offered ships for evacuation have also been contacted but did not immediately respond by the time of publication.
While the majority of people evacuated before the first eruption, the cruise ships called to help evacuate 136 farm workers stranded on the island after a flight was cancelled from the first explosion. They arrived in St Lucia on Saturday, according to the Associated Press
“Anybody who would have not heeded the evacuation, they need to get out immediately," Erouscilla Joseph, director of the University of the West Indies’ Seismic Research Center, told the outlet.
While the volcano last erupted in 1979, Mr Joseph said the latest explosion is equivalent is the event of 1902 that killed about 1,600 people.
Mr Gonsalves, who had not evacuated himself, had planned to meet with government officials on Monday to discuss the island's food supplies.
Up to three dozen people were reported to have stayed behind in an area of the island called Sandy Bay.
“It is over time for you to leave,” he said. “It is dangerous.”
Deputy prime minister Montgomery Daniel told NBC Radio the damage was worst in the northeast of the island, where farms and crops were wiped out.
“What I saw was indeed terrible,” he said after a tour of the region on Sunday.
Additional reporting by the Associated Press