Shuttle buses have temporarily replaced Red Line service on the MBTA between the North Quincy and JFK/UMass stations due to a power problem, according to MBTA officials.
Customers are being encouraged to use the Commuter Rail from Braintree and Quincy Center to South Station.
Authorities said a track maintenance vehicle derailed earlier this morning on the southbound side which caused the delays. That equipment has been removed but MBTA crews are still on the scene working.
Service is expected to resume at about 6 a.m.