Andy Burnham’s successor as Greater Manchester mayor will be announced on Friday in what is his first electoral test as prime minister.
Counting of votes from Thursday’s by-election will begin at 9am and continue throughout the day. The result is not expected to be declared before the afternoon.
More than two million people were eligible to vote in the contest, triggered by Mr Burnham’s election as MP for Makerfield last month before he became leader of the Labour Party.
Polling before the vote suggested Labour candidate Bev Craig, currently the leader of Manchester City Council and an ally of Mr Burnham’s, was on course to win by a comfortable margin.
Her main rival is likely to be either Reform UK’s Sian Astley or the Green Party’s Geraldine Coggins, who are likely to battle it out for second place.
Mr Burnham voted at a polling station in Golborne, near Wigan, late on Thursday, casting his ballot less than an hour before polls closed.