Police have seized more than 200 cannabis plants after a house fire in Sydney's southwest.

Police and emergency services found a fire in the ceiling of the lounge room about 10pm (local time) on Thursday.

Inside, they allegedly discovered the Bonnyrigg Heights home was being used to grow hydroponic cannabis.

Officers from Strike Force Zambesi seized 208 cannabis plants with a potential street value of $695,000 AUD.

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Investigations were continuing.

-AAP