Sunak said earlier on Friday that he called Labour Party leader Kier Starmer to congratulate him on the victory in the parliamentary election.
"I will now head down to London, where I will say more about tonight's result, before I leave the job as prime minister, to which I have given my all," UK broadcaster Sky News quoted the prime minister as saying.
The leader of the party that wins the parliamentary election becomes the country's prime minister and forms a new government.