Emergency officials in Manawa, Wis., were rescuing people stranded on flooded roads on Friday after a river overflowing from torrential rain spilled over a local dam.

The Little Wolf River began overpowering the Manawa Dam around 12:30 p.m. local time after the area near the dam received more than five inches of rain in about four hours on Friday morning, said Kurt Kotenberg, a meteorologist at the National Weather Service in Green Bay, Wis.

Emergency officials were rescuing drivers who had become stranded while trying to flee, Mr. Kotenberg said. “People were in cars on roads that were flooded,” he said. Some were rescued “standing on the hoods of their cars,” he added.

As of Friday afternoon, Mr. Kotenberg said there had been no reports of deaths or injuries from the flooding.

Heavy rain in the Midwest in recent weeks has drawn attention to the vulnerability of dams in the region. The Rapidan Dam in southern Minnesota came close to failing last month.

The Manawa Dam is near the northern side of the Wisconsin city, on the edge of the Manawa Mill Pond. The city, home to roughly 1,400 people, is about 50 miles west of Green Bay. Mr. Kotenberg said it would take time to determine whether the dam had cracked.

In an advisory, the Weather Service urged Manawa residents to seek higher ground if possible. Mr. Kotenberg clarified that residents should try to do so while sheltering in place and not try to flee by flooded roads.

In a message posted on Facebook, the Waupaca County Sheriff’s Office said rescue personnel were “diligently working” to help vulnerable people in Manawa and urged residents to avoid entering the city.

In another message, officials urged residents in the affected area to boil tap water before drinking it, saying “the public should assume the water is unsafe to drink due to contaminants.”