A situation at Muni's Castro Station Monday afternoon involving a person in the trackway is likely to delay both inbound and outbound service in the Muni Metro tunnel.

Muni announced the presence of "an intruder in the tunnel near Castro Station" around 2:30 pm Monday, which was prompting a "safety check" and some slow-moving train service.

A tipster subsequently has told SFist that the person was struck by a Muni train and injured at or near Castro Station, but appeared to be alive. The collision has not yet been confirmed.

The San Francisco Fire Department tweeted that they are "assisting a person with an isolated injury" at Castro Station.

At 2:42 pm, Muni tweeted an update, saying "Until the intruder can be removed, [outbound Muni service] will be held at Castro Station." The agency added that inbound K, L, and M trains may be temporarily switching back at West Portal Station.

This is a developing story.