The death toll in Haiti has escalated to more than 300, officials have said, following Hurricane Matthew's destructive campaign across the Caribbean.

A senator from the south of Haiti told AFP that more than 300 had died. A Reuters estimate using figures reported by local civil protection officials put the death toll even higher, at at least 478.

The majority of those killed were in towns and fishing villages along the southern coast of Haiti, and access to the south-west of the country was restricted after the collapse of a major bridge.

The Category Four storm headed for the southeastern coast of America and today hit Florida, carrying winds of 120 miles per hour and causing 600,000 homes to lose power.

Matthew is the first major hurricane to threaten a direct hit on the US in more than a decade. It has now been downgraded to Category Three but still poses a major threat.

In Haiti – the poorest country in the western hemisphere – thousands of people have been displaced and aid organisations are already on the ground helping those worst hit.

Samaritan's Purse, which is headed by evangelist Billy Graham's son Franklin, has sent a disaster assistance team to join its Haiti staff in an emergency response. It has also sent a plane loaded with emergency supplies including clean water, sanitary items and plastic sheeting for emergency shelter.

"Hurricane Matthew has wreaked havoc on Haiti," said Graham. "Our teams are on the ground helping in Jesus' Name. They're going to do all they can to meet the needs of the suffering people there. Please pray for the people of Haiti as they recover from this deadly storm."

On US soil, Samaritan's Purse said it is contacting church partners in Florida, Georgia, South and North Carolina to help mobilise volunteers.

Christian charity World Vision also has a team on the ground in Haiti, and has launched an appeal for £8 million to help children and families affected by the disaster.

John Hasse, national director of World Vision's programmes in Haiti, said the situation was "desperate".

Another World Vision staff member said banana fields – the livelihood of many Haitians – had been destroyed.

David Bell, UK humanitarian operations manager at World Vision, said: "Hundreds of thousands of children are in desperate need of relief aid in the areas worst hit by Hurricane Matthew in southern Haiti. Our teams together with other aid agencies are on the ground trying to reach all of them. However, three days after the storm, we are not sure how many of them need urgent assistance. This is because the damage to road infrastructure and transport networks continues to hamper our assessment and relief efforts."

The immediate needa are water, shelter, sanitarian assistance and medical help, Bell said.

"Many families are now exposed to the elements because of the sheer number of houses damaged and destroyed. 80 per cent of homes in the south of Haiti are reportedly damaged and nearly 16,000 people are staying in temporary shelters. This puts children at risk because we now have to help protect them while their parents are restoring their livelihoods.

"We would like to urge the British and international public to support our appeal. This appeal will ensure that World Vision can help meet the needs of the most vulnerable especially children."