At least 19 people killed and thousands still at risk of flooding and power outages as US begins clean-up in wake of devastating Hurricane Matthew

AMERICA has started the colossal clean-up following Hurricane Matthew amid warnings that deadly flood waters could threaten more lives after at least 19 Americans were killed.

Officials in several states in the south east of the country have warned that flooding could continue as swollen rivers crest in the coming days.

Matthew, the most powerful Atlantic storm since 2007, was downgraded to a post-tropical cyclone on Sunday after its rampage through the Caribbean killed 1,000 people in Haiti.

In the United States, the death toll rose to at least 19 people.

While power was being restored in some areas, 1.6 million people were without power in Florida, Georgia, North and South Carolina and Virginia, down from Sunday's peak of 2.2 million.

Authorities were working to clear streets of fallen trees and abandoned vehicles.

With five people reported missing and rivers rising, North Carolina Governor Pat McCrory said he expected the death toll to rise.  Eight people in the state have already lost their lives.

McCrory said several swelling rivers were expected to hit record levels and would not crest for days.

"Hurricane Matthew is off the map, but it is still with us and it is still deadly," he said.

The National Weather Service said "life-threatening flooding" would continue on Monday over eastern portions of the state.

Many coastal and inland communities remained under water, either from coastal storm surge or overrun rivers and creeks.

In neighbouring South Carolina, a vehicle trying to cross a flooded roadway in Florence County was swept away by flood waters, killing one person, Governor Nikki Haley said.

In Virginia Beach, the city said it had received over 13 inches of rain and 55,000 people remained without power on Sunday night. The city said that some 200 vehicles were abandoned and many roads remained impassable.

Norfolk, which declared a state of emergency, said efforts were under way to clear streets of debris and abandoned vehicles with city offices, libraries and recreational centers set to re-open Monday.

U.S. President Barack Obama declared a state of emergency in Georgia and Florida, freeing up federal money to help the states repair damaged infrastructure and remove debris.

The killer storm claimed an estimated 900 lives when it smashed through Haiti.

The Caribbean country is now starting the clean-up operation amid fears of a cholera outbreak.

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