On Monday, 70.2 per cent of the votes had been counted with Liberal candidate and Belmont councillor Glenys Godfrey taking a 0.5 per cent lead over Labor candidate Cassie Rowe.
Electoral Commissioner Warwick Gately said the outcome of each electorate would not be finalised until at least Friday because postal votes did not close until Thursday.
Whether known as Belmont or Ascot, as it was prior to the 1989 election, the electorate has always been held by Labor and was represented by retiring MP Eric Ripper for the past 25 years.
The 7 per cent swing to the Liberal Party was a surprising outcome for the supposedly safe Labor seat, however it followed a trend of increased support for the incumbent government in the metropolitan area.
WA Electoral Commission communications manager Justin Harbord said Belmont was one of the closest seats in the election and would be the focus of the commission over the coming weeks.
The seats of Collie-Preston, Eyre, Kimberley and Midland are also currently undecided.
To follow the results of the Belmont electorate, visit the electoral commission website at www.elections.wa.gov.au/results.