A house fire in Sydney's north-west has led police to more than $500,000 worth of cannabis.

Emergency services were called to the house on Goodhall Avenue in Baulkham Hills about 4:00am (AEDT) yesterday.

Fire crews put out the flames and alerted police to a hydroponic set-up in the house.

Police examined the house and found 281 cannabis plants plus 250 grams of the drug and hydroponic equipment.

They say the drugs seized have an estimated street value of more than $550,000.

Witnesses have told police they saw a man driving away from the house around the time the fire started.