Tropical Storm Hanna closed in on the southeastern US Thursday after hammering Haiti and was expected to surge into a hurricane, even as explosive Hurricane Ike gathered force in the Atlantic.

Hanna "has been an erratic storm. It's already done a lot of flooding (and) we are expecting it to strengthen slightly" before Friday, when it is due to pound the US states of North or South Carolina, US National Hurricane Center forecaster John Cangialosi told AFP.

Helicopters plucked desperate survivors from rooftops in the flooded Haitian city of Gonaives after Hanna claimed at least 61 lives, the third major storm to pound the poorest country in the Americas in as many weeks.

Meanwhile a monster storm over the Atlantic Ocean, Hurricane Ike, turned into an "extremely dangerous" category four storm on the five-level Saffir-Simpson scale, the hurricane center reported.

The storm, the fifth of the 2008 hurricane season, was moving across the Atlantic hundreds of miles from any land with winds of 215 kilometers (135 miles) per hour. It was too early to predict if "land areas might eventually be affected," the NHC said.

"It is absolutely a powerful hurricane (but) there is no immediate threat" to land, Cangialosi said. He said it was too soon to tell if it would track toward the US eastern coastline, or westward toward the Gulf of Mexico.

"Just keep your eyes on it," Cangialosi warned.

As of 0900 GMT, Hanna was moving northwest and was expected to pass east of the central and northwestern Bahamas on Thursday "and will be near the southeast coast of the United States by Friday or Friday night," it said.

Hanna had maximum sustained winds of about 110 kilometers (70 miles) per hour and rain bands and tropical storm force winds swirled as far as 465 km (290 miles) from its center early Thursday.

A hurricane watch was in effect from Surf City in North Carolina to north of Edisto Beach on the South Carolina coast, the hurricane center said.

As meteorologists monitored Hanna and Ike, vast flooding in Haiti revived memories of lethal Tropical Storm Jeanne in 2004, when about 3,000 people were killed, mostly in the northern city of Gonaives.

The UN peacekeeping mission in Haiti (MINUSTAH) carried out dramatic helicopter rescues to save those stranded by the high water.

"We have managed to recover two dozen people who were trapped on rooftops," MINUSTAH spokeswoman Sophie Boutaud de la Combe told AFP, adding that nine injured people were flown to the capital for treatment.

Mountainous Haiti is especially prone to flooding and landslides due to widespread deforestation on its section of the island of Hispaniola, which it shares with the Dominican Republic.

Tens of thousands of people in both countries were forced to take refuge due to the driving rain and flooding, though there were no casualties reported in the Dominican Republic.

Hanna struck Haiti one week after it was hit by Hurricane Gustav, which killed 77 people. Two weeks ago, Tropical Storm Fay sparked flooding in Haiti that left about 40 people dead.

As Hanna churned, the government of the Bahamas downgraded its hurricane watch to a tropical storm warning, while the US embassy in Nassau announced it would be closed Thursday and Friday.

Officials at Grand Bahama hospitals said they were confident they could handle any emergency.

A third storm, Josephine, was reported in the eastern Atlantic 605 kilometers (375 miles) west of the southernmost Cape Verde islands at tropical storm strength, but was expected to weaken as it moved west-northwest Thursday.