Part of Green Line B Branch service is being replaced by shuttle buses after a trolley derailed near Packard’s Corner in Allston, the MBTA said.

Roughly 30 passengers were aboard when the derailment occurred around 1:40 p.m. Monday, and were able to safely exit the westbound train. There were no injuries, MBTA spokesperson Joe Pesaturo said.

Riders are being told to expect delays as buses are dispatched.

“Buses are replacing B branch service between Kenmore and Washington Street while T personnel work to re-rail the trolley car,” Pesaturo said. “The cause of the derailment is under investigation.”

The derailment was reported to both T oversight agencies, the Department of Public Utilities and the Federal Transit Administration.

Initially communicated by the T as a “disabled train near Packard’s Corner,” follow-up tweets from the agency later said that delays were being caused by a trolley that had, in fact, derailed.