(Reuters) - Heavy rains pounded northern Minnesota on Wednesday, forcing the evacuation of dozens of homes, causing mudslides and sinkholes, and swamping a zoo where several animals died and a polar bear briefly escaped, officials said.

The flooding in the Duluth area, a port on Lake Superior, was the worst the city had seen in four decades, officials said.

"The last time there was something similar was in 1972," said Duluth police spokesman Jim Hansen.

The sheets of rain turned some hillside roads into rivers that tore up roadways, popped off manhole covers and flooded the Lake Superior Zoo, where several barnyard animals died, including a donkey, sheep and goats.

"It's pretty devastating," said Kara Gilbert, an office support specialist who was answering telephones at the zoo. "We can all look out and see half of the zoo under water."

The zoo's polar bear, Berlin, exited her exhibit and was tranquilized by the zoo's vet and quarantined, the zoo said. Two seals also escaped their enclosures but were captured.

"A few of the animals got out of their enclosures, but they are contained and doing fine," Gilbert said.

Five to 9 inches of rain fell overnight and rain continued on Wednesday with a flash flood warning in effect until 10:30 p.m. CDT (0300 GMT) for parts of the region, the National Weather Service said.

About 250 residents left 80 homes in Duluth's Fond du Lac neighborhood, and 40 residents were cleared from the town of Thomson, about 18 miles southwest of Duluth. Two campgrounds also were evacuated.

No deaths or serious injuries were reported as a result of the heavy rains and flooding.

Numerous roads in Duluth and the surrounding area were under water, and parts of area highways and Interstate 35 in Duluth were impassable. Officials warned residents to stay off the roads, and said the standing water was likely unsanitary.

EMERGENCIES DECLARED

Minnesota Governor Mark Dayton and Duluth Mayor Don Ness declared emergencies and the Red Cross opened shelters. The National Guard could be deployed if needed under Dayton's order, and the governor planned to tour flooded areas on Thursday.

The general cargo terminal at the Port of Duluth-Superior closed at midday on Wednesday due to concerns about the safety of crews getting to and leaving the facility, said Adele Yorde, public relations manager for the Duluth Seaway Port Authority.

"I've been in Duluth off and on for almost 40 years, and I've never seen rain like this," Yorde said, adding that, "We're used to snow and ice up here. Not this."

Port employees expect to return to work on Thursday, she said.

CHS Inc said it had suspended loading operations at its Superior, Wisconsin, grain terminal, the largest at the port, due to heavy rains and expected to resume on Thursday.

Canadian National Railway Company freight lines across Minnesota and northern Wisconsin were shut due to the rain and flooding, spokesman Patrick Waldron said.

The railway runs about 25 trains per day carrying freight that includes grain and iron ore through those corridors and it was sending crews out to check on the trains and for areas of the tracks that may need repairs, Waldron said.

The Jay Cooke, Savanna Portage and Moose Lake state parks were closed until further notice because of the flooding, the state natural resources department said.

About 350 Minnesota Power customers were without power on Wednesday because of flooding, and the company was passing the increased water flows on the St. Louis River through its dams, a process that can take several days, officials said.

"Our gates are wide open and passing the maximum amount of water they can," said Bonnie Carlson, Minnesota Power's hydro operations manager, who said there was no threat to the dams.