Emergency services were called to the fire on Cressy St at about 1.40pm today.
Fire Risk management Officer Wayne Hamilton said crews arrived to find the lounge of the house fully involved in fire.
But a vehicle was blocking the nearby fire hydrant.
"It is a reminder for people, especially in Lyttelton, but anywhere to check first and not park in front of hydrants."
He said early indications show the house did not have working smoke alarms but that has not been fully confirmed.
"If the fire had occurred at night, it could easily have been fatal.
"It's not ideal at all."
Hamilton said the fire was contained at about 3pm and a fire investigator was sent to the scene.
A St John spokesman said they were called to the fire but were not required.
"Our volunteer crews did an excellent job," Hamilton said.
