Early results in a state by-election that could have ramifications for the leadership of Queensland's Labor opposition show a neck and neck contest.

The race for Stafford, in Brisbane's inner north, is shaping up to be a photo finish for the LNP's Fiona Hammond and the ALP's Luke Richmond.

With a tad over 60 per cent of the vote counted at 9pm on Saturday, there appeared to be a swing towards the LNP but the result was expected to depend on preference flows.

ABC News has said the outcome was too tight to predict during the evening update.

'I am trying to make a projection of the result in a few different ways and my estimates are all hovering with Labor somewhere between 49.5-51 per cent,' Chief Elections and Data Analyst Casey Briggs said.

'That is to say, it's close!'

With preference counts still to come in five polling places and in both early voting centres, the flow of figures had slowed significantly by mid-evening.

Stafford has been held by Labor for most of its history but suffered an eight per cent swing against it at the last state election in 2024.

The by-election was triggered by the sudden death of former independent MP Jimmy Sullivan, who was expelled from the Labor Party last May over legal and medical concerns.

Polls closed at 6pm, with more than 14,000 people casting their ballots on Saturday.

Almost 42 per cent of electors chose to vote early, with 13,530 in person and 3,860 by post.

Electoral Commissioner Pat Vidgen said staff were counting first preferences from votes cast on election day, during early voting, telephone voting and the postal votes returned so far.

'Voting finished at 6pm... but it could still take a few days to determine the results,' he said.

'We'll only declare successful candidates when the outcome is certain.'

Pauline Hanson's chief of staff earlier defended One Nation's decision not to stand a candidate, saying it would have been a waste of resources.

James Ashby told AAP the short four-week campaign did not give the populist conservative party enough time, adding:  'I don't want to burn candidates.'

'Why would you put a huge amount of resources and effort into a four-week campaign? I want our candidates to have a year.'

Political expert Paul Williams said a win for the LNP would have ramifications for David Crisafulli's government, Labor and federal politics.

The Griffith University political scientist said Ms Hammond was likely to snatch the seat with a predicted vote of 51-52 per cent after preferences.

Prof Williams also said One Nation had made an error by failing to field a candidate in the urban seat, where the party has historically struggled for traction.

'They wouldn't win it but six months ago it would have been impossible and now it's moved from impossible to unlikely,' he said.

He said One Nation might have polled between 12 and 20 per cent - or even more, almost guaranteeing an LNP victory on preferences.

But Ashby said One Nation had no interest in boosting the LNP's fortunes in the city.

'We're not here to prop the LNP up, just like they're not here to prop us up,' he said.

With by-election swings towards a sitting government rare, Prof Williams said even a reduction in Labor's 5.3 per cent margin would technically be a loss for Labor and former premier Steven Miles.

Mr Miles said on Friday the contest was an opportunity for voters in the seat to send the Crisafulli government a message.

He said the outcome of the election would not affect the government or the Labor Party's leadership.