West Australian Labor has held former premier Mark McGowan’s seat in a by-election viewed as a test of new premier Roger Cook’s leadership.

Mr Cook’s popularity crashed in recent weeks according to a poll showing the Liberal party holds a 54 per cent to 46 per cent two-party preferred lead over Labor.

But it wasn’t enough to unseat the party in Rockingham, south of Perth, where Mr McGowan’s replacement, Magenta Marshall polled 49.41 per cent of the vote.

With a little over 22,000 votes counted late on Saturday, Labor was headed toward a two-party preferred vote of 65.2 per cent.

The party’s healthy margin of 37.7 per cent, forged by Mr McGowan’s popularity in 2021 amid the COVID-19 pandemic, is expected to fall to 30.4 per cent.

Liberal Party candidate Peter Hudson, who campaigned on crime, health care and inflationary pressures, polled 17.73 per cent of ballots.

Ms Marshall was selected as Labor’s candidate over Deputy Mayor of Rockingham Hayley Edwards, who ran against Ms Marshall as an independent and received 16.01 per cent of votes.

Rockingham is a coastal community about 50 kilometres south of Perth city, with some 30,000 voters registered.

Controversial Aboriginal heritage laws, the rising cost of living and housing shortages added to Labor’s woes in the run-up to the by-election, which was viewed as a test of Mr Cook and WA Liberal leader Libby Mettam’s leaderships.

Mr McGowan retired from politics in May citing exhaustion.

— AAP