After a Green Line derailment near Lechmere station in Cambridge sent seven people to the hospital Tuesday, the MBTA moved to replace the line with shuttles as federal and state investigations examine the cause of the incident.

The MBTA said Wednesday it is not yet clear when regular service will resume on the Green Line as crews have not yet cleared a train that derailed in Cambridge.

The buses will run between North Station and Medford/Tufts and Union Square in Somerville, the MBTA said in a post on social media early Wednesday morning.

Train service on the entire Green Line Extension will be shut down "until further notice" while MBTA crews and federal investigators determine the cause of -- and damage from -- a Tuesday afternoon derailment.

Shuttle buses are continuing to replace service on the MBTA’s Green Line in Cambridge and Somerville, a day after a train derailed, sending seven passengers to hospitals with minor injuries. In all, 50 people were on board the Green Line train headed east when it derailed as it passed over a track switch between the Union Square and Medford/Tufts branches of the line,