PHILADELPHIA -- An off-duty police officer shot an erratic driver early Monday morning in South Philadelphia, CBS Philadelphia reports. Police said the driver of a black Honda was shot as he attempted to run over pedestrians.

Around 7:30 a.m., the driver struck and injured at least one pedestrian and attempted to mow others down with the Honda. Police say a concerned citizen pinned the driver in with their SUV.

An off-duty police captain who happened to be nearby approached the scene and the suspect tried to attack him, police said. The officer then pulled his service weapon and shot the driver in the head, according to police.

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"I just heard, 'Pop, pop, pop, pop, pop,' and knew something was going down," said witness Marc DiBattista.

The driver is reported to be in extremely critical condition.

The pedestrian who was struck was taken to the hospital and did not appear to have life-threatening injuries, police said.

An off-duty police officer shot an erratic driver in South Philadelphia who police say was trying to run over pedestrians early on Jan. 29, 2018. CBS Philadelphia

At this time, authorities are not releasing the officer's name. They are only identifying him as a detective with the Philadelphia Police Department who is assigned to the Major Crimes Division.

The driver's identity is also being withheld. Police say he had a Virginia driver's license and the Honda had Maryland license plates on it.

The motive for the incident is under investigation.