More than 90 people have cast invalid votes after the wrong ballot papers were delivered to polling stations in Stockport.
Stockport Council said people in Heatons North had voted for candidates in Heatons South and vice versa, between 0700 and 0710 BST.
The mistake was discovered at 0710 BST and correct papers were delivered by 0900 BST, the local authority said.
The council said it was trying to reach people to ask them to vote again.
It said it would provide transport to get people to polling stations if they needed it and advised them to get in touch.
Deputy Returning Officer Laureen Donnan said: “We apologise to everyone who was inconvenienced in Heatons North and Heatons South early this morning.
“We spotted the error very quickly, and we are taking all steps possible to ensure the situation is rectified.”
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