Two cars destroyed in arson attack at family home in Sydney's south-west

A manhunt is underway tonight after a group of men set two cars on fire outside a family's home in Sydney's south-west.

Police say the attack was a targeted firebombing but have not yet established a motive.

The cars were set alight in the driveway of the home on San Cristobal Drive in Green Valley at 12.50am today.

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The family inside the home, two parents and two children, managed to escape the flames, which spread to a small section of the home.

Firefighters weren't able the save the cars but did manage to protect the home from further damage.

Neighbours say they spotted four men at the time of the fire.

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Others told 9News the area was usually quiet.

"It's a beautiful quiet area so it's very strange something like this has happened," one said.

Witnesses also told 9News one of the men set himself on fire during the alleged arson attack.

Police are investigating the alleged arson attack.