Officials shut down the First Hill Streetcar system Wednesday after a mechanical issue was identified prompting officials to inspect the fleet of six seven Czech-designed cars that serve the line.

The service stopped serving riders mid-Wednesday afternoon. The first announcement of the disruption came from King County Metro, the agency that operates the City of Seattle service, just before 3 PM Wednesday. An announcement early Thursday morning confirmed the line was still not operating.

Transit Alert – First Hill Streetcar service is interrupted. Use alternate Metro bus rts 7, 9, 36 or 60, or Link light rail. — King County Metro (@kcmetrobus) March 1, 2017

A King County spokesperson told CHS Wednesday night that a mechanical issue was identified in one of the streetcars prompting officials to pull all of the cars back to the service facility on 8th Ave S in the International District. The spokesperson said he did not yet have additional information about the nature of the issue.

The First Hill Streetcar began service in January in 2016 after months of delay. The start of service on the line was bogged down, in part, by longer-than-expected testing on the propulsion system designed specifically for the First Hill line. The system uses regenerative braking during downhill sections in order to power special batteries allowing streetcars to periodically detach from their overhead wires so they can travel alongside city busses. The system was developed for the First Hill Streetcar to reduce overhead wire conflicts with the Metro trolley buses.

In 2015, CHS reported more details of some of the issues that caused the rollout of the service to be delayed including “water-damaged inverters.”

The Seattle Department of Transportation says that around 3,000 riders utilize the First Hill Streetcar daily. UPDATE 3:25 PM: Metro is operating a shuttle (PDF) to partially cover some of the streetcar’s route.

Wednesday, SDOT also said its announcement of changes to Broadway to help speed up service on the notoriously slow-paced streetcar route was premature and that planned changes to the street won’t happen until after more “analysis and outreach.” A department spokesperson told CHS that SDOT plans to begin that outreach this summer.

UPDATE 5:50 PM: A spokesperson said he still could not provide information on the nature of the mechanical issue but it must be serious. The First Hill Streetcar will not be in service again on Friday.