Officers responded to the incident at The Embarcadero between Piers 5 and 7 and the other at Sacramento and Drumm streets around 4:15 a.m., according to police.
A man and woman were transported to San Francisco General Hospital, police said.
The man was stabbed in the chest and is suffering from life threatening injuries, police said.
The woman, who was stabbed in the leg and back, is in stable condition, according to police.
Police are on scene investigating the stabbings and no arrests have been made.