A pedestrian was killed in a collision with a semi truck at Fifth and Market early Thursday morning. And the truck reportedly fled the scene.

Bay City News tells us via the SFPD that the accident was reported at 5:42 a.m., and no description of the truck has yet been given.

The deceased victim has only been described as "an adult," but the Chronicle suggests via evidence at the scene that the person was elderly or disabled — the paper reports, "A mangled walker lay at the corner of Fifth and Market streets, with clothing and a single shoe strewn in the roadway." Supervisor Matt Haney confirmed to the Chronicle that the victim has died from their injuries.

The investigation prompted an alert about police activity in the area.

KRON4 reports on a second active investigation scene at Broadway and Front Streets where the big rig may have been located. The video below shows the red truck, and police are reportedly underneath it, seeking evidence.

We'll update you as more information is available.

This post has been updated to reflect that the victim has died.