The New York Times reports the worker had crawled into the space - just 37 inches high - to load baggage when another baggage handler apparently closed the cargo compartment door Monday.
The Federal Aviation Administration said in a statement that the plane's co-pilot heard "yelling and pounding" from the cargo area.
The FFA said the handler was also assigned to operate the tug that pushes the plane back from the gate, and workers waiting to move the plane noticed the tug driver was missing.
The worker was freed unharmed and the flight left for Hartford, Conn.
Information from: The New York Times, http://www.nytimes.com