The fiercest Caribbean storm in almost a decade has ripped into Haiti's southwestern peninsula 230km/h winds and storm surges, killing at least one person and damaging homes.
The eye of the violent and slow-moving Category 4 storm was hovering over the western tip of Haiti on Tuesday, the US National Hurricane Center said, pounding coastal villages with strong gusts.
One man died as the storm crashed through his home in the beach town of Port Salut, Haiti's civil protection service said. He had been too sick to leave for a shelter, officials said. One fisherman was killed in heavy seas over the weekend as the storm approached, and another was missing.
Overnight, Haitians living in vulnerable coastal shacks on the Tiburon Peninsula frantically sought shelter as Matthew closed in, bringing heavy rain and gusts and driving the ocean into seaside towns. Several districts in southern Haiti were flooded, with crops inundated with ocean and rain water.
About a metre of rain is forecast to fall over hills that are largely deforested and so more prone to flash floods and mudslides, threatening villages as well as shanty towns in the capital Port-au-Prince, where heavy rain fell overnight.
More than 9000 people were huddled in shelters across Haiti, authorities said.
Life-threatening flash floods and mudslides were likely in southern and northwestern Haiti, the hurricane center said.
It expected Matthew to remain a powerful hurricane through at least Wednesday night.
People in Haiti, the poorest country in the Americas, are often reluctant to leave home in the face of storms, fearing their few belongings will be stolen.
Authorities moved around 1000 inmates from at least four prisons to safer locations outside the storm's path, officials said.
The strongest Caribbean storm since Hurricane Felix in 2009 threatens to linger long enough for its winds and rain to cause great damage in Haiti, where it will spend much of the day before hitting Cuba and the Bahamas later on Tuesday.
It could reach Florida by Thursday as a major hurricane, although weaker than at present, the hurricane center said.
In Cuba authorities have spent days organising teams of volunteers to move residents to safety and secure property.
The storm is expected to make a direct hit later on Tuesday in the province of Guantanamo, which is home to the disputed US Naval base and military prison and also to a small Cuban city. The US Navy ordered the evacuation of 700 spouses and children of service personnel as the storm approached.