He also says reports that his relationship with Mr Turnbull has broken down are false.

Mr Turnbull will attend an oceans conference in Bali on October 29-30, despite criticism from some government backbenchers including former deputy prime minister Barnaby Joyce and ex-leader Tony Abbott.

"Eight weeks ago when I met with President (Joko) Widodo and he indicated to me that the former prime minister had expressed his willingness to attend that summit," Mr Morrison told parliament on Wednesday.

The prime minister said the Indonesian president warmly welcomed Mr Turnbull's attendance, given their personal history.

"We thought it would be a good opportunity if the former prime minister were able to attend that summit, given their very strong close working relationship," he said.

"The decision was taken weeks and weeks ago. I believe it was the right decision for Australia."

Mr Abbott, who has been appointed a special envoy for indigenous communities, said a current government minister should attend.

"The important thing is to send a minister because only a minister can represent the government," Mr Abbott told 2GB radio.

He said Mr Turnbull had always been "emissions focused" - having lost the Liberal leadership twice over climate policy - and would put a particular point of view to the conference.

Mr Joyce said the move was "pretty wild", especially given Mr Turnbull did not campaign in the Wentworth by-election on behalf of candidate Dave Sharma.

"Now I'm on the backbench I can tell you the truth: it is a problem and there should have been a bit more thought put into this, I don't think it's the right move," Mr Joyce said.

Mr Morrison said all prime ministers, from both side of politics, had a role to play in serving the national interest when they are able.

"I don't think Malcolm's hanging around looking for a trip to Bali," Mr Morrison told reporters.

Wentworth is likely to fall to independent candidate Kerryn Phelps, who has a solid lead in the vote count.

Australian Associated Press