Who is popular today?

Polls have opened in the Western Australian state seat of Rockingham in what will be an early test for Premier Roger Cook.

The by-election was sparked after the resignation of former Premier Mark McGowan.

Labor holds the seat on a 37.7 margin and is one of the safest in the state.

Party strategists are predicting the margin to drop, as by-elections generally record a swing against the government of the day.