(Reuters) - A rash of incidents Monday afternoon involving envelopes sent with suspicious white powder had police scrambling around New York City and forced the nation's fourth-biggest bank, Wells Fargo & Co, to shut down five branches around the city.

In one of six cases identified by the New York Police Department, the substance turned out to be corn starch, a police spokesman said. The substance has not yet been identified in the remaining five cases, the spokesman said.

The Wells Fargo branches will remain closed pending further investigation by the police, bank spokesman Ancel Martinez said. The branch locations include Third Avenue and 47th Street; Madison Avenue and 34th Street; and Broadway and 85th Street.

More than 500 protesters demonstrated at the bank's annual shareholder meeting in San Francisco last week to express anger over foreclosures, executive compensation and corporate taxes.

Among other large banks, spokesmen for Bank of America Corp and JPMorgan Chase & Co said they had not closed any branches on Monday due to suspicious envelopes. A Citigroup spokesman had no immediate comment.

According to a website called maydaynyc.org, demonstrations are planned in New York City on Tuesday against "the corporations who rule our city."

San Francisco-based Wells Fargo is the fourth-largest U.S. bank by assets.

(Reporting by Edith Honan and David Henry in New York and Rick Rothacker in Charlotte; Editing by Eric Walsh)