Authorities say a man who was freed from a space between two walls of a Colorado department store may have been there for several days yelling for help.

Paul Felyk was rescued by firefighters using a circular saw to cut into the side of the building, Longmont police said. Employees at the Marshalls store reported hearing someone shouting but could not tell where it was coming from.

The next day, employees found the man yelling through a hole in the wall, so they notified authorities.

Longmont fire department spokeswoman Molly Meehan said Mr Felyk entered the building through a vent on the roof for "unknown reasons".