Firefighters responded to a report of a fire at a home in the 2900 block of Aetna Way at about 3:45 a.m., San Jose fire Capt. Reggie Williams said.
The fire was found in the rear of the structure in a patio enclosure, Williams said.
Two residents -- a male and female -- were inside the home at the time of the blaze and had a difficult time escaping, according to Williams.
There were bars on all the windows and exterior doors, and the residents escaped the home through the rear where the fire was burning, Williams said.
Williams said the two residents suffered "critical burns" and were transported to a hospital for treatment.
The fire has since been knocked down but had not yet been deemed under control as of 6 a.m., according to Williams.
Williams said an arson investigator was at the residence, which is now considered a crime scene. The captain did not say why it is being considered a crime scene.
Further details were not immediately available.