Donald Trump Jr has called on his father to 'fight to the death' over the presidential  election as he echoed his unfounded claims of voter fraud and cheating after Trump's leads in Pennsylvania and Georgia slipped further.

The president's eldest son made the comments on Thursday as he spoke at a news conference at the Georgia Republican Party Headquarters in Atlanta. 

'I think the number one thing Donald Trump can do in this election is fight each and every one of these battles to the death so that we get full transparency in the process,' Don Jr said. 

'And everyone on the Democrat side should welcome this unless they are actually cheating.' 

Don Jr cast doubt on the counting process, accusing Democrats of ignoring election deadlines, claiming boxes of invalid ballots 'magically' appeared in Democratic states and counties after voting had ended. 

'We know that's against the law, but you get in front of a Democrat judge in a Democrat city with Democrat control and it's okay,' he said.