Suspected Good Samaritan carjacker nabbed

A man who allegedly carjacked a 'Good Samaritan' on Perth's Mitchell Freeway has been caught by police.

The 30-year-old man was found by police at a Morley home just hours after the offence on Friday morning, and taken into custody.

The 35-year-old victim, a construction worker who wanted to be known only as Chad, said he was still wiping the sleep from his eyes when he saw a car engulfed in flames.

Other witnesses saw the driver, who had fled the crash, walking through traffic erratically with an injured arm before he stole Chad's white Rodeo ute, which still had the keys in it.

Chad said the man who stole his uninsured ute, which has been recovered by police, was a "low life".

"I wouldn't mind going a couple of rounds with him," he said.

But he would still stop to help a person in need.

Detective Constable Steven Waddell said Chad did the right thing by stopping to help.

The early-morning wreck caused major peak hour traffic delays but has since been removed.