Howard joins Hastie on campaign trail

Former Prime Minister John Howard says he is a "compulsive campaigner" and his presence in the federal seat of Canning does not indicate the Liberals are worried about losing the by-election.

Mr Howard was at a Mandurah shopping centre with Liberal candidate Andrew Hastie on Thursday and said he was always happy to help his "good friend" Tony Abbott and his government.

"I happened to be coming over to Western Australia and I couldn't resist offering myself to help, and he's such an impressive candidate that I wanted to sort of be part of the action," Mr Howard told reporters.

"It's really got nothing to do with desperation. I'm always happy to help Tony Abbott."

Mr Howard said long-serving Liberal Don Randall, who previously held the seat before his sudden death in July, had been a friend of his and Mr Hastie would be a good successor.

He added that the by-election should be less about sending a message to the prime minister and more about telling Labor leader Bill Shorten to stop obstructing a free trade agreement with China.