Investigators said the haul from the robbery outside a Wells Fargo bank was more than $300,000, WPVI-TV reported. At least four men appear to have been involved, escaping in a minivan they abandoned nearby.
No arrests had been made late Thursday.
Marnan Harner, who was working in a hairdressing salon across the street, said the guard told her at first he thought the robbers were carrying out a Halloween joke, KYW-TV reported. But Edward Hanko, special agent in charge for the FBI, said it was clearly no joke.
"The timing of such, the armored car arriving at a certain time, would just indicate that it was preplanned and well planned," Hanko said. "One masked subject ordered the guard to the ground while pointing a gun at him and the other subject went for the money."
Investigators said the abandoned van had been reported stolen in August. The robbers apparently escaped in another car.