NEW YORK (AP) — Federal authorities are investigating what might have caused a commuter train to derail in New York City, killing four people and injuring more than 60 others.

The National Transportation Safety Board is probing Sunday's fatal Metro-North train crash. The agency says its investigators will spend up to 10 days looking into the crash.

Authorities say the train was rounding a riverside curve early Sunday when it derailed, toppling cars and throwing some riders from their seats.

The Metropolitan Transit Authority warned commuters of crowded trains on Monday morning. It says it's providing shuttle buses and urged commuters who are able to work from home to do so.

The MTA oversees Metro-North, the nation's second-biggest commuter railroad. On an average weekday, about 26,000 commuters ride the affected Metro-North line.

(Story by: Associated Press Reporters Kiley Armstrong and Verena Dobnik)