The death toll from historic flooding in the United States state of Louisiana went up to eight on Tuesday, as the expanding flood zone prompted authorities to declare disasters in a dozen parishes.

While waters were receding in parts of southern Louisiana,other areas were seeing rising waters. The National Weather Service issued renewed flood warnings.

"We're seeing unprecedented flood levels as the waters move south," Louisiana Governor John Bel Edwards said at a news conference.

Officials said 40,000 homes have been impacted by the floods, and more than 8,000 people were in shelters.

More than 20,000 have been rescued or evacuated, they said.

A dozen parishes -- similar to counties in other states --have now been declared emergency disaster areas, up from four on Monday.

Waters were receding in some northern and western areas of the flood zone, while other areas were still in an active emergency, the governor said.

IMAGE: Residents use a boat to navigate through flood waters in Ascension Parish, Louisiana. Photograph: Jonathan Bachman/Reuters