Propane tanks on the motorhome exploded and the fire quickly spread up the grassy hillside helped by current dry conditions in the Lower Mainland, fire officials said.
"Because it was in the middle of the bypass, they ran out of water at one point and we had to actually attack it in the housing development above," said Port Coquitlam Fire Chief Nick Delmonico.
It took crews over an hour to contain the blaze, he said.
"We actually had a number of area residents who had their sprinklers and hose lines out and were actually providing a bit of value putting some water on the area up top as well," he said.
No one was injured, but westbound traffic was backed up past the Pitt River Bridge and eastbound traffic was snarled.