Malcolm Turnbull's personal popularity looms large over the upcoming Wentworth by-election, with some voters pledging to punish the Liberals for ousting the former prime minister.

Key points: Mr Turnbull is popular in his electorate and holds the seat with a higher margin than most other Liberals in Sydney

Mr Turnbull is popular in his electorate and holds the seat with a higher margin than most other Liberals in Sydney Antony Green predicts the Liberals will suffer a 4-5 per cent swing against them just because Mr Turnbull is no longer the candidate

Antony Green predicts the Liberals will suffer a 4-5 per cent swing against them just because Mr Turnbull is no longer the candidate A ReachTel poll of 800 voters has the two-party preferred vote locked at 50-50

Mr Turnbull has held the seat in Sydney's affluent eastern suburbs since 2004 and won it with a 17.7 per cent margin at the last election.

He has announced plans to resign from the Parliament on Friday, after being dumped from the nation's top job in a Liberal leadership spill last week.

According to the ABC's election analyst Antony Green, Mr Turnbull's vote had gone up more than most other Liberal electorates in Sydney since his election, thanks to his popularity and high profile.

"His vote is significantly higher than the Liberal vote in the Senate, which suggests that the swing against the Government at the by-election will be … maybe 4 to 5 per cent just [based on] the fact that Malcolm Turnbull's no longer a candidate," he said.

A ReachTel poll published this morning — funded by the Australia Institute with a sample size of 886 residents — found the Liberals' margin has been completely eroded, with Labor and the Liberals now neck-and-neck.

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Small business owner Ian Nessick, who has lived in the electorate for almost 30 years, said he would vote for the Liberal Party if Mr Turnbull was in the running, but was now considering the Greens.

"He [Turnbull] was a decent, civilised sort of guy," he said, describing him as more "worldly" than other Liberal politicians.

"Now Australia is the new South Africa. We're going backward at a rapid pace.

"And that new guy, Scott Morrison, what did he do? He quotes Bono in his [first] speech as Prime Minister."

Ian Nessick says he would have voted for the Liberal Party in the next election if Malcolm Turnbull was still running. ( ABC News: Jennine Khalik )

The by-election is expected to take place next month in the electorate that includes some of the country's most leafy suburbs — Paddington, Bondi, Point Piper and Vaucluse.

So far, Christine Forster, a City of Sydney councillor and former prime minister Tony Abbott's sister, has confirmed she will be running for Liberal preselection.

The former Australian ambassador to Israel, Dave Sharma, is also running in the preselection, along with Andrew Bragg, who ran the Liberals' Yes campaign throughout the same-sex marriage plebiscite.

'I might be voting Labor for the first time in 50 years'

"They [Liberals] have lost my vote," local Barbara Jones told the ABC.

"I might be voting Labor for the first time in 50 years. I'll have to see if there'll be a strong independent candidate."

Ms Jones, walking down Oxford Street before dusk, said she was "disillusioned" with the Liberal Party.

"I didn't like him [Turnbull] the first time round, but then I did like him," she said.

"When they started the debacle, I couldn't see anyone better than Malcolm Turnbull. Certainly not Dutton. I didn't like his values, like [the issue of] same-sex marriage."

Yet Paddington resident Sam Keogh said nothing would change with a Labor government and he "always voted along party lines".

"No way I'm having Bill Shorten as my prime minister," he said.

Jeff Errington said he was voting for the Greens, but Mr Turnbull's resignation made little difference to him because "I've never voted Liberal".

Lambrini Kates, a longtime local, describes the leadership spill as "pretty frightening". ( ABC News: Jennine Khalik )

Lambrini Kates, who has lived in Bondi and its surrounds for 30 years, said she was not voting for the Liberals, but relative to other politicians in the party, Mr Turnbull "looked good".

She felt Australia was following the United States with more conservative politicians in power.

"Turnbull had more middle views, and he was pulled into trying to please and appease the right wing," Ms Kates said.

"Julie Bishop seemed more popular and I preferred her to them. [But] I'm not inspired by any of them [the parties]."