NEW ORLEANS – The Army Corps of Engineers closed a gate on a suburban canal as heavy rains lashed the flood-prone city, raising fears that climbing waters threatened the walls holding them back.

After more than 8 inches of rain fell on parts of New Orleans by late afternoon, Mayor Ray Nagin shut City Hall early, and schools also closed. People were asked to stay indoors until the flood potential subsided. More rain was expected overnight.

The Harvey Canal in Jefferson Parish was one of several in the area placed under new safety guidelines after Hurricane Katrina’s flood waters breached two New Orleans canals in August 2005, causing catastrophic flooding.

The corps has worked to strengthen the canal, about five miles from downtown, but engineers worried that water being driven into it might lead to flooding. The area around the canal includes homes and businesses.

Engineers want to be sure “that we don’t put pressure” on the flood walls, said Amanda Jones, a corps spokeswoman.

Water accumulated quickly in some older neighborhoods, a reminder of the city’s vulnerability to storms and reliance on a complicated system of pumps and canals for drainage.

Water nearly got into the Prytania Theater in the Uptown neighborhood, a cultural icon and favorite refuge for Ignatius J. Reilly, the antihero in John Kennedy Toole’s novel “A Confederacy of Dunces,” said Eric Ramstead, the theater’s manager.

Despite the flooding potential, the rain also offered relief to parts of Louisiana that have been abnormally dry.