Police are looking for two people seen fleeing from a house fire in Sydney's northwest where a hydroponic drug set-up was found.

Emergency services were called to the home at Carlingford about 7.30pm on Monday night where they found the property well alight.

Once the blaze was extinguished officers found a large number of cannabis plants inside, police said.

An elaborate hydroponic set-up with more plants was also found in a storage area underneath the house.

A neighbour who lives near the home, named only as Scott, saw the incident unfold.

"I saw some smouldering from the roof. I saw the two owners running out of the house into their cars and then they sped off in haste," he told the Fairfax Radio Network on Tuesday.

Witnesses have told police they saw a woman leaving the vicinity of the home in a dark grey BMW sedan, and a man leave in a grey Toyota Hilux ute.

Anyone with information is urged to call Crime Stoppers on 1800 333 000.