Major flooding in Duluth, Minn.

DULUTH, Minn. (AP) - Residents evacuated their homes and animals escaped from pens at a zoo as floods fed by a steady torrential downpour struck northeastern Minnesota, inundating the city of Duluth, officials said Wednesday.

Police officers helped track down a polar bear that got out of its enclosure overnight at the low-lying Lake Superior Zoo where several animals drowned.

Duluth Mayor Don Ness declared a state of emergency after the deluge of up to 9 inches of rain that he said caused extensive damage to the port city of about 86,000. Some neighboring communities did the same. Ness said the order would start the process to obtain federal aid, and Gov. Mark Dayton said he would travel to Duluth on Thursday to discuss how the state can help.

There were no immediate reports of serious injuries, though an 8-year-old boy was swept about six blocks through a culvert in Duluth. The boy suffered some scrapes and bruises but was fine, St. Louis County Undersheriff Dave Phillips said, calling it a "miracle out of this whole disaster."

Much of Duluth is spread along a steep rocky hillside overlooking Lake Superior so the water speeds downhill, carrying debris with it, Ness said.

"There are certainly reports of streets being washed out, but the more significant problems are as the water comes over the ridge and starts rushing down the hill, overwhelming our storm systems, overwhelming our culvert system and creating that forward momentum of rushing water," Ness said. "That's where the most significant problems are being felt."

• Click here to see photos of the flooding
• Click here to see FOX 11 Meteorologist Doug Higgins' in-depth look at the flooding

The zoo lies at the foot of the hill, making it particularly vulnerable. Several sheep, goats and a donkey in the barnyard exhibit were killed by the flooding, said Susan Wolniakowski, director of guest services. It also provided an opportunity for Berlin, a female polar bear, to escape.

"Even though it's a large white object, it's pretty nerve racking," police spokesman Jim Hansen said of the chase for Berlin. Zoo officials said she was tranquilized by the zoo's vet and placed in quarantine.

Peter Pruett, the zoo's director of Animal Management, said the "entire staff is devastated" at the loss of the animals.

Two seals managed to swim out of the zoo but were quickly recaptured just outside. Wolniakowski said no dangerous animals left the zoo grounds and that all have been secured.

"I think it's probably been the worst flooding we've ever had at the zoo," Wolniakowski said. The zoo's train depot was completely underwater, she said.

Ness said it may take time for the damage to become fully apparent. He said the volume of rain in a short period puts a tremendous amount of stress on sewer and road systems.

"We're concerned about washouts and sinkholes and they'll likely show themselves in the coming days. ... The water is rushing so hard that we're concerned about the integrity of the roadbeds being washed out," he said.

Several major highways leading into the city were closed because of the flooding and authorities encouraged residents to stay home due to the volume of standing and rushing floods, and the difficulty in spotting hazards under water, such as missing manhole covers.

"It's a mess. There are too many intersections to even list that are closed," Hansen said.

Authorities asked residents of the low-lying Fond du Lac neighborhood to leave their homes because of the rising level of the St. Louis River. Hansen said about a dozen homes were evacuated.

"Fortunately ... it is a relatively small number of households that are being evacuated," Ness said. "Most homes in Duluth are farther up the hill."

The Red Cross opened two shelters for evacuees. The University of Minnesota Duluth campus closed Wednesday but planned to reopen Thursday.

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Associated Press writers Steve Karnowski and Jeff Baenen in Minneapolis and Gretchen Ehlke in Milwaukee contributed to this report.