British Prime Minister Keir Starmer has announced he will step down as leader of the Labour Party but will remain as caretaker prime minister until a new candidate is elected.

Following mounting pressure within the party for a change in leadership, Starmer has begun the process of mapping out a timeline to hand over power.

His departure comes after the former Greater Manchester mayor Andy Burnham, a favourite to replace Starmer, won a local election to gain a seat in the House of Commons.

"Every decision I have taken has been about putting the country I love first. That is why I will resign as leader of the Labour Party," Starmer said as he choked up in an emotional speech outside 10 Downing Street.

Starmer said the process of picking a new Labour Party leader would be launched in July and he would remain as prime minister until his successor is chosen, to be in place in September.