With buildings submerged, roads washed out and rivers surging, authorities declared emergencies on Wednesday and ordered hundreds of thousands of people evacuated in New Jersey, New York, Maryland and Pennsylvania.

By Thursday afternoon, the threat of further damage appeared to have passed, although officials said it would take time for the water to recede.

"In terms of the flood, the worst of it is over. But we still have a long way to go in terms of cleaning it up and getting people back in their houses. The clean-up is going to be massive," said Trenton Mayor Doug Palmer.

Up to 200,000 evacuees from the historic coal-mining region around Wilkes-Barre, Pennsylvania, were allowed to return to their homes and businesses after levees held back the Susquehanna River, which crested overnight.

"Had the dikes broken, we could have had a New Orleans type situation in Wilkes-Barre," said Pennsylvania Gov. Ed Rendell, praising emergency services for their work which included rescuing 1,200 people by helicopter, raft and other means.

Levees failed in New Orleans last year after Hurricane Katrina, flooding 80 percent of the city.

Rendell said it was too soon to assess the damage, which he called "incalculable." "Yesterday was a war zone in the northern tier of Pennsylvania," he said on CNN.

MILLIONS IN DAMAGE

New Jersey Gov. Jon Corzine told reporters the flooding was likely to cause damage in a similar range to floods last year that caused losses amounting to US$30 million.

Trenton Police Capt. Joseph Juniak said the Delaware River was lower than had been predicted by afternoon. "The worst of it is over," he said.

"The hardest part after this will be getting the residents back in there," he said, adding that it could take a week.

There were 6,200 people evacuated from homes along the Delaware, Corzine said. Those who remained were urged to conserve water because floods had forced the closing of a filtration plant, leaving just a day and a half's supply of water until it was fixed.

Angela Ellis, 44, from the Island section of Trenton, asked police if she could go home, saying, "You mind if I swim into my property and grab a few belongings and swim out? All my stuff is in there."

Melvena Barnes, 26, and her one-week-old daughter, who left their apartment near the river to stay with her mother, vowed this flood was her last. "I'm moving," she said. "I've been here for four years, and the floods just keep getting worse."

New York Gov. George Pataki said after visiting the flooded city of Binghamton the destruction was unprecedented and the cost could run into hundreds of millions of dollars, according to a spokesman.