After escaping a car that crashed into the Nashua River, an 8-year-old Fitchburg boy scrambled up a steep embankment and walked more than a mile home to get help for his father, who was trapped in the wreckage.

The car landed upside-down on a sandbar in the rushing river after crashing through a guardrail on Oak Hill Road shortly after 3 a.m. Thursday, authorities said. With his father trapped, the boy climbed some 20 feet back up to the road and found his way home, where he woke his mother up to call 911.

Both the father and the son escaped the crash without serious harm.

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“It’s amazing anyone’s alive,” said Brian Belliveau, the city’s deputy fire chief. The car hurtled through the guardrail and into the air, landing on a sandbar about 15 feet offshore. Belliveau said speed was likely a factor in the crash.

Responders were able to extricate the father from the car without incident.

Belliveau said the boy showed great poise under the circumstances.

“He walked a good 20 minutes home in the middle of the night,” he said.

Police were not immediately available for comment about the accident.