CHARLESTON, United States: Relentless rain left large areas of the US southeast under water Saturday and forecasters warned that more heavy downpours could trigger historic flooding in the crucial next 24 hours.

The states of North and South Carolina have been particularly hard hit, but the driving rain in recent days has spared almost none of the US East Coast and forecasters say the worst is not over quite yet.

News reports blamed the wild weather on four deaths in the United States since Thursday, all in the Carolinas.

It is a separate weather system from Hurricane Joaquin, a powerful Category Four storm that battered the Bahamas, destroying homes, and was threatening to do much the same to Bermuda.

South Carolina Governor Nikki Haley has warned of the possibility of record-setting rainfall over the weekend and President Barack Obama on Saturday issued an emergency declaration for the state, ordering federal aid for areas affected by flooding.

Some streets were submerged in the historic old town of Charleston, South Carolina, an AFP reporter said.

Most of the restaurants and bars were closed because of the rising water.

“We are used to flooding in the area but this is extraordinary,” said police sergeant Edwin Graceley.

John and Merroli Haas, tourists from Kansas, took shelter from the heavy rain under the old market hall.

“We were going to go to Savannah (in neighboring Georgia) today but we decided not to. We didn’t want to take the chance,” Merroli said.

Power was out in parts of South Carolina and Haley reiterated her call for drivers to keep off the roads over the weekend for their own safety.

The National Weather Service warned of “potentially historic and life-threatening flooding” across the southeast of the United States.