A 12-year-old boy steered his family's car to safety along a US highway after his father suffered what appeared to be a seizure while driving, then brought his younger sister to safety behind a guardrail while waiting for help.

The boy, who's from Dracut, Massachusetts, took the wheel at the weekend, steered it into a southbound breakdown lane in Peabody and applied the brakes, state police said. He then used his dad's cellphone to call emergency services.

He told the dispatcher that his father was having a seizure while driving on the highway, state police said. He didn't know where he was or what road he was on, but was able to describe landmarks. Officials were only able to narrow the location to Peabody, about 32 kilometres north of Boston, by tracking the cellphone signal.

State police say the search was difficult because there are several highways in the area, but troopers found the family shortly after the boy called 911.

The boy's father, who was unconscious, was brought to a local clinic and is reported to be in good condition.

"The Massachusetts state police want to commend the quick thinking and courageous actions of this young man," state police said in a statement.

Authorities haven't released the names of the boy and his father.

- AP