Hurricane Matthew made landfall in Haiti on Tuesday morning as an "extremely dangerous" Category 4 storm, unleashing life-threatening winds and torrential downpours on the poorest nation in the Americas, according to dpa. As of 2 pm (1800 GMT) the US National Hurricane Centre said the storm's eye was located over the Windward Passage between Haiti and Cuba, with maximum sustained winds of 230 kilometres per hour as it moved north at 17 kph. After crossing over Haiti, the hurricane's course has it approaching eastern Cuba by late Tuesday. By Wednesday forecasters said Matthew could begin striking parts of the Bahamas as it is expected to turn north-west. Hurricane watches now extend to the US state of Florida, where the governor has declared a state of emergency. A planned appearance on Wednesday by US President Barack Obama at a rally for Democratic Party presidential candidate Hillary Clinton in Miami was postponed due to the approaching storm. Obama will instead visit the Federal Emergency Management Agency (FEMA) in Washington for an update on storm preparations. On Haiti there were reports of washed out bridges and roads rendered impassable by floodwaters and downed trees. Caribbean nations have been on alert since Matthew strengthened into a hurricane last week and then briefly intensified into a Category 5 storm at the weekend, becoming the strongest in the Atlantic since 2007. Evacuations have taken place across Jamaica, Haiti, Cuba and elsewhere, with residents of low-lying areas told to leave their homes and to expect storm surges, flash floods and mudslides. Parts of Haiti could experience 101 centimetres of rainfall, the US hurricane centre said. The World Meteorological Organization in Geneva warned Tuesday that Haiti is the nation most vulnerable to Hurricane Matthew. It noted that the last Category 4 storm was Hurricane Flora in 1963, which was one of the deadliest hurricanes to hit the region. About 80 per cent of Haiti's population lives below the poverty line, according to US statistics, many residing in flimsy shelters susceptible to toppling. The UN World Food Programme (WFP) said it was preparing to come to the aid of affected countries. In Haiti, WFP has enough emergency food stockpiled in positions across the country to feed up to 300,000 people for one month. "Our priority is to support the governments' interventions to save lives and meet the food needs of the most vulnerable and food insecure people affected," said Miguel Barreto, WFP Regional Director for Latin America and the Caribbean, in a statement. UN children's agency UNICEF said that "life-saving supplies for 10,000 people are in place and ready to be distributed to the most affected families in the worst hit areas." The US has sent disaster response teams to Jamaica and Haiti the White House said. At least three deaths - one each in Haiti, Colombia, and Saint Vincent and the Grenadines - have been connected to the hurricane, according to local officials and media reports. Cuban authorities have evacuated about 1 million people from coastal regions, while the US Navy has ordered the evacuation of about 700 non-essential staff from its base at Guantanamo Bay.