The man somehow got through a gated area at the Brink's facility in Southwest Philadelphia shortly after 7 a.m. Thursday and grabbed the cash, police said. Guards caught him as he tried to run, police said.
The name of the 33-year-old man was not immediately released. It was not clear whether he was a Brink's employee or just posing as one, a police spokeswoman said.
Ed Cunningham, a spokesman for Richmond, Va.-based The Brink's Co., declined to comment.
No one was injured in the attempted robbery, police said.