GOLDEN, B.C. - An 11-year-old boy from Edmonton has lost his parents and two sisters after a devastating long-weekend crash along a mountain highway in British Columbia that killed six people.

The victims were all members of two families that had split up in separate cars as they travelled from Edmonton to Abbotsford in B.C.'s Lower Mainland.

As they drove along a stretch of highway east of Golden, a small community located about 250 kilometres west of Calgary, the minivan drifted into oncoming traffic, slamming head-on into an RV and killing everyone inside.

The victims' names weren't released, but the RCMP said they included four members of one family, including a mother, a 47-year old father and two girls aged 13 and 15. The 11-year-old boy from that family was travelling in a second vehicle that wasn't involved in the crash.

A 14-year-old girl from the second family and her grandfather were also in the minivan, and they were both killed. The grandfather was not a Canadian citizen, police said.

Sami Monir, a friend of both families, said the boy had switched vehicles so the 14-year-old daughter from the other family could ride along with his older sisters. Monir identified the father who died as Arshad Mahmood, and the 14-year-old girl from the second family as Elizeh Shah.

Monir said he was in Abbotsford with a friend waiting for the two families to arrive when a truck driver phoned them with news of the crash. They immediately drove to Golden, where they met the young boy and the father of the other family.

"He's 11 years old. He was holding spirits pretty high," Monir said in an interview.

"He was very confident. He came out and met us and basically thanked us for visiting him. He was actually giving us the courage because we were all really devastated."

Monir said the boy is staying with the Shah family until relatives arrive from Pakistan and Dubai.

RCMP Cpl. Dan Moskaluk said police are helping the family contact relatives back home, and will connect them with any local agencies that can offer assistance.

"We have an 11-year-old child who has now lost his entire family," RCMP Cpl. Dan Moskaluk said in an interview. "The highest priority now is dealing with and assisting with the families involved."

Investigators had ruled out speed, alcohol and road conditions. The van will also be inspected this week for any signs of mechanical failure.

But accounts from witnesses, who said the van appeared to drift into the lane of oncoming traffic without any attempt avoid the RV, led police to focus on driver fatigue or inattention as possible factors, said Moskaluk.

"It didn't move slowly, it tended to slowly drift over -- that's indicative of a person who has fallen asleep or a person who is inattentive," said Moskaluk.

"When a person is conscious, there is usually a reaction and a correction, that being an application of brakes or a steering correction. In this case, witnesses said the vehicle had simply drifted over."

Two people in the RV were treated for non-life-threatening injuries.

Moskaluk said four of the six people in the van weren't wearing seatbelts, but the crash proved too severe even for the two who were buckled in.

A photograph of the scene released by the RCMP showed the twisted wreckage of the minivan in the middle of the highway. The RV was sitting several metres away, with a large section below the windshield ripped off and scattered along the pavement.

Golden Mayor Christina Benty said she was in church Sunday morning when she heard the blare of sirens rush past, heading east out of town on a busy section of highway that has seen more than its share of deadly collisions over the years.

"We just heard siren after siren after siren, and we know this was bad," recalled Benty.

"We hear the sirens going out of town on a regular basis, and every time we do, there is a collective lurching in the stomach. ... Being a community on the No. 1 Highway, we hear the sirens too often."

The winding Trans-Canada Highway around Golden has a reputation as an especially treacherous section of roadway, listed by the Canadian Automobile Association as one of the 12 most dangerous spots in the country.

However, based on the RCMP's description of where the accident occurred and their photograph of the scene, Benty said it appears the crash wasn't on the most dangerous part of the highway located just outside of town.

She noted investigators hadn't singled out the condition of the highway as a potential factor in the crash, which occurred on a straight section of road.

"It (the apparent crash site) is not that initial maybe 10 kilometres outside of Golden that's just twisty and turny through the Kicking Horse Canyon there," she said.

"It is a well-travelled highway, a lot of Albertans travelling into B.C. for holidays."

The federal and B.C. governments are currently funding a $970-million highway upgrade between Golden and the Alberta boundary.