Knockout punch in SF’s Mid-Market leaves man in critical condition

File photo of emergency room sign. Red Emergency Sign at Hospital File photo of emergency room sign. Red Emergency Sign at Hospital Photo: Steven G. De Polo / Getty Image Photo: Steven G. De Polo / Getty Image Image 1 of / 43 Caption Close Knockout punch in SF’s Mid-Market leaves man in critical condition 1 / 43 Back to Gallery

San Francisco police are searching for a 30-year-old man who punched another man and left him with life-threatening injuries Monday evening in the Mid-Market neighborhood.

The aggravated assault occurred at 7:19 p.m. on Jones and Market streets, authorities said. The victim, who is in his 30s, fell on the ground and was taken to a nearby hospital in critical condition.

Police do not know what led to the altercation and are actively investigating, said Officer Robert Rueca, a San Francisco police spokesman.

Gwendolyn Wu is a San Francisco Chronicle staff writer. Email: gwendolyn.wu@sfchronicle.com Twitter: @gwendolynawu