The blaze started just after 8 a.m. in a two-story home on Bismark Street near Mission Street.
"The first company found the building charred with smoke and they forced entry," said Todd Johnson, Daly City Fire Battalion Chief.
Investigators say firefighters saw flames coming from the kitchen and the house was filled with heavy smoke.
"Two victims found inside the house and both were transported to the local hospital in critical condition," said Fire Chief, Johnson.
Firefighters pointed to smoke detectors partially to blame for the fire.
"It appears that smoke detectors may have played a role in this. Delay detection," said Fire Chief, Johnson.
According to neighbors the two people in critical condition are a father and his child.
Riki Kim lives two doors down and said, "We were in shock because we've seen those kids riding their bikes sometimes out here," said Kim.
Firefighters remained on scene for over four hours preventing a broader spread.
"Devastating. It's really devastating and sad and specially to think that the alarms were to working," said Daly City Resident, Heidi Elias.
The cause is under investigation but firefighters emphasized making sure people have working smoke detectors in their homes.
They say there was "delayed detection" with this fire.
No firefighters were injured and the fire division and Daly City police are investigating the cause of the fire.