People had to rescued from cars in Bexon on St Lucia
At least eight people died and dozens were forced out of their homes by heavy rain in the Caribbean islands of St Vincent and the Grenadines.
Prime Minister Ralph Gonsalves has cut short his holidays and was returning from London, the government said.
Landslides and flooding also reportedly killed five people in the neighbouring island of St Lucia.
Heavy rain has also been causing destruction in Dominica, also in the eastern Caribbean Sea.
The region was expected to remain on rain alert, according to meteorological services.
Mr Gonsalves said he couldn't remember such heavy rain at Christmas.
It had been raining all day across St Lucia, but by early
evening on Christmas Eve we were seeing sheet rain.
We were on our way to the airport to get a flight back to
London Gatwick when waters started to rise very quickly
in the residential area of Bexon, just south of the capital
We had to abandon our car and seek shelter on higher
ground. Several families were huddled together watching
the waters rise.
Several men were going from car to car and house to
house making sure people were safely out. We saw some
people being rescued from their flooded homes in an
emptied refrigerator which was used as a boat.
Waters reached about 1.5m (five feet) in depth.
Some local residents told me this was worse than the
flooding seen in 2010 during Hurricane Thomas, but at
least there weren't the strong winds this time.
'It came down heavy'
A woman who lives in Canada and was spending her holidays with her family in St Vincent told reporters how she got separated from her sisters and ended up losing one of them and her two-year-old niece.
"We all were going together, but the water came down heavy and it just turned us over," Colleen James told news website I-Witness Online. The extreme weather hit St Vincent on Christmas Eve, with many seeking refuge in shelters as the flooding began.
A family of five died when a house was washed into their home in the north-western region of North Leeward, local media reported.
The rain also cut off the water supply of about half of the island, authorities say.
An official government notice said Mr Gonsalves was returning from his holiday in London, where he was staying after a visit to Rome, where he met Pope Francis.
In St Lucia a policeman was killed while reportedly trying to save people who were in difficulty, after torrential rain on Christmas Eve.
Midnight religious services were cancelled and churches in the island's capital Castries were used as shelters for people displaced by flooding.
Local media reports say at least another four bodies have now been found.
St Lucia's Prime Minister Kenny Anthony said: ``I don't think I can recall when we have had such heavy rainfall on the eve of Christmas."