The river is expected to crest at 31 feet Thursday, 4 feet higher than the previous record set in 1979, said Joseph Hewitt of the National Weather Service. Downriver in New Brunswick, hundreds of people left their homes.
During a conference call, scientists described the flooding on the St. John as a "greater than a 100-year event," Maine emergency management spokeswoman Lynette Miller said.
"It's certainly a dangerous situation. That's why they're doing evacuations proactively," she said.
The St. John had risen so much that the International Bridge between Fort Kent and Clair, New Brunswick, was closed during the night amid fears that the racing water could drag it down.
"We're evacuating all the main streets, going to all the businesses and telling them to close up for safety," Fort Kent police Chief Kenneth Michaud said.
A bridge over the Fish River, which empties into the St. John in the town of about 4,200, also was closed as a precaution.
Emergency officials in New Brunswick warned people living along the St. John River to brace for the worst flood in decades, with up to 1,300 homes threatened by the rising water. By Wednesday afternoon, more than 300 people had registered with the Red Cross to confirm they have left their homes or plan to do so.
That number was expected to grow as officials warned that floodwaters would continue to rise until Thursday morning, when the crest in the Fredericton area would likely reach a level just below the record set in 1973.
Crews in Fredericton cleared out the basement of the New Brunswick legislature, removing pictures of politicians dating back to the early 1800s, and sandbags were piled around the base of the Victorian-era legislature complex.
Evacuations also took place along the St. John River in Van Buren, downstream from Fort Kent, and in the Penobscot County town of Mattawamkeag due to the Mattawamkeag and Penobscot rivers spilling over their banks, according to the weather service. Evacuations were ordered in the northern Maine town of Washburn downstream from two dams in danger of breaching.
In addition to the heavy rain this week, there had still been a half-foot of snow on the ground following a winter that dumped around 200 inches of snow in the region.
"In response to that, a lot of these rivers took off," Hewitt said. The St. John is expected to remain above flood stage through Friday, he said.
Late Tuesday, Maine Gov. John Baldacci issued a state of emergency for Aroostook County because of flooding in the Fort Kent and Wallagrass areas.
