The stabbing occurred at an apartment complex on S. Euclid Avenue around 9:30 a.m., according to Pasadena city officials. The victim was listed as being in critical condition.
Mayfield Junior School was placed on lockdown as authorities searched for the attacker in the surrounding area near the school. Residents were instructed to avoid the area or shelter in place.
The lockdown was lifted around 2:30 p.m., police said.
The suspect was said to have a dark complexion, large build and wearing a green trench coat, and he should be considered extremely dangerous, city officials said.
Euclid and Los Robles avenues were shut down between California and Del Mar boulevards amid the search.
A motive for the attack and any possible association between the victim and suspect remains under investigation.