Alex Turnbull has lashed out at the factions within the Liberal Party that helped sink his father's prime ministership urging voters to reject the party at the upcoming Wentworth by-election.

Appearing on a Facebook video ahead of the October 20 vote, the Singapore-based fund manager said the Liberal Party had been taken over by "extremists" of the hard right.

The by-election in the Sydney seat was called following his father's resignation as a result of a leadership coup which saw Scott Morrison assume the prime ministership.

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"This (leadership spill) isn't exactly a first for Australian politics, but it does lead you to the conclusion that a stable government might not be as stable as some people would like you to think," he said.

"To me, this particular event seems to show the Liberal party has been taken over, frankly from extremists on the hard right who aren't particularly motivated to win an election and aren't particularly motivated to serve the general public - they just want to pursue a crazy agenda."

But Mr Morrison said Malcolm Turnbull doesn't agree with his son.

"I disagree with Alex. His father disagrees with him too," Mr Morrison told the ABC on Friday.

"His father Malcolm Turnbull is heavily supporting Dave Sharma, the only Liberal candidate running for Wentworth."

Mr Morrison says the former prime minister has recently been silent on the issue as he has bowed out of public life.

The younger Turnbull said, "smaller Liberals" such as himself were very upset and conflicted because there wasn't anyone "reasonable to vote for" within party ranks.

"Here's the thing about the Wentworth by-election and we're going to have an election in 12 months anyway, so if you want to send a signal as to which way the Liberal Party is going and your displeasure as to where it is going, this is your opportunity," he said.

"Don't vote for the Liberal Party at the Wentworth by-election. If you want to pull the Liberal Party back from the brink, it's the one clear signal you can send."

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He also turned his attention to the party's energy policy, months after his father's National Energy Guarantee was rejected.

"As an investor in energy, I've seen that in particular there is no way coal can compete anymore, renewables have gotten too cheap, firming costs are reasonable, and really there is no trade-off anymore to lowering your power bills and reducing emissions," he said.

"And still some would like to prosecute a cultural war over this issue for whatever their reasons may be."

In September, Alex Turnbull announced on social media that was going to solicit funds for the Labor candidate in Wentworth.