"I've never seen flooding like this before," said Faustino Melo, 40, a resident in the hard-hit Massachusetts city of Peabody, a suburb north of Boston whose downtown streets were submerged with floodwaters that rose as high as door handles.

Emergency crews steered boats along streets to help evacuate people, while National Guard soldiers set up checkpoints to block off roads. About 200,000 sand bags were used to hold back overflowing rivers across Massachusetts.

About 12 to 15 inches (30 to 38 cm) of rain has fallen since Friday, swelling the Merrimack River that runs through southern New Hampshire and Massachusetts more than 8 feet (2.4 metres) above flood stage -- its highest since 1936.

"It's bad now but we're expecting it to get much much worse," said Massachusetts Emergency Management Agency spokesman Peter Judge, citing weather forecasts for more rain on Monday night with several rivers still rising.

"Right now we're looking at all of the rivers, from the Charles River in the Boston area all the way north and east to the Merrimack River on the New Hampshire border. We expect all of those rivers to reach and exceed flood stage in the next 24 hours," Judge said.

THOUSANDS EVACUATED

Several thousand New Hampshire residents had been evacuated from homes and more than 600 roads in the state had been closed, the New Hampshire Bureau of Emergency Management said.

A bulging dam in Milton, New Hampshire on the Maine border was in danger of failing and could send a 10-foot (3-m) wall of water downstream, the National Weather Service said.

About a thousand people were evacuated from their homes in the Massachusetts' suburbs of Melrose, Haverhill, Lawrence and Peabody, where flooding caused sewage to back up into cellars and sinks, rescue workers said.

About 35 million gallons a day of sewage was flowing into the Merrimack River in Haverhill, while another 115 million gallons a day were expected to spill in from a treatment plant in the city of Lawrence, said Massachusetts Gov. Mitt Romney.

Romney said damage across the state was expected to exceed US$7 million, a threshold for federal assistance. "It's going to get worse before it gets better," he told a news conference, adding that he was concerned about the stability of bridges and dams pressured by the storm water.

The torrential rain has turned May into the second-wettest month since records began in 1872, with about 10.75 inches (27.3 cm) of rain -- more than triple the monthly average of 3.2 inches (8.1 cm) -- falling in Boston midway through the month, said Charlie Foley, a meteorologist at the National Weather Service.

The storm, which had moved up from the Gulf of Mexico, is expected to be followed by two other storm systems both moving east off the Great Lakes region on Tuesday that will dump 1 to 3 inches (3 to 8 cm) more water, said Foley. It is the biggest downpour to hit the region since October 1996, he added.