Image copyright AP Image caption Much of Charleston, South Carolina, is already under water

US President Barack Obama has declared a state of emergency in South Carolina, as heavy rainfall is set to lead to more flooding over the weekend in many parts of the east coast.

It has been raining for much of the week, but a weather system connected to Hurricane Joaquin in the Caribbean is expected to make the situation worse.

It is regaining strength and has been reclassified as a category 4 storm.

Joaquin, currently off the Bahamas, has winds of up to 155mph (250 km/h).

The storm is not expected to hit the eastern US, but the moisture associated with it is contributing to heavy rainfall, particularly in South Carolina.

The US National Weather Service says parts of the state could see over 15 inches (380mm) of rain by Sunday evening.

In the historic city centre of Charleston, many streets have been closed and sandbags have been piled up to keep floodwaters out.

"Where we normally are dealing with flooding for a few hours, we're dealing with it in days here,'' Charleston Police Chief Greg Mullen told the Associated Press news agency.

The emergency declared by President Obama means state and local authorities can receive federal help to deal with the flooding.

On Thursday a cargo ship, named the El Faro, went missing after sailing through Hurricane Joaquin off the Bahamas.

Rescue teams searching for the vessel and its 33 crew said on Saturday they had found a life belt believed to belong to the ship.