A seriously injured 12-year-old has been allegedly abandoned at a fiery car crash scene by two men, one of whom was carted away from the site in a shopping trolley.

NSW Police said they were later forced to use a stun gun on a dog as they tried to help paramedics treat the injured trolley traveller as the incident evolved in Sydney’s western suburbs.

The Thursday-night incident in Cranebrook began after a stolen car smashed into a tree and burst into flames shortly before 7.30pm.

The boy, suffering a broken leg and hip injuries, and two men were helped out of the wreck by passers-by.

Before emergency services arrived, one of the men walked from the crash scene while another was taken from the scene by two men using a shopping trolley.

Paramedics were called to a nearby home soon afterwards for that injured man.

They sought police help to force entry to the property to treat the distressed man, sparking a confrontation with two other men inside.

Those men, aged 40 and 55, were sprayed with capsicum spray and police stunned a dog with a Taser.

The injured man was later found and taken to Westmead Hospital for treatment on a broken leg and head lacerations.

He has also undergone mandatory testing.

The men aged 40 and 55 were arrested and charged with hindering police.

Both the 12-year-old boy and the other man are in a serious but stable condition.

The dog was uninjured and left in the care of a neighbour, police said.

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