Joe Biden is on track to become the Democratic presidential nominee as he won all three states which voted on Tuesday, piling pressure on Bernie Sanders to drop out of the race.

The former US vice president took Florida, Arizona and Illinois, extending his delegate lead over Mr Sanders and making the latter’s path to victory exceptionally narrow.

All three states were won so comfortably that they were called for Mr Biden shortly after polls closed. In Florida and Illinois he secured around 60 per cent of the vote.

Mr Biden has now won 19 states to Mr Sanders's seven. The clean sweep on Tuesday triggered fresh calls for Mr Sanders, the Vermont senator, to concede defeat and withdraw.

There were signs that Democrats trusted Mr Biden more than Mr Sanders to tackle coronavirus.

Exit polls showed two thirds of respondents picked Mr Biden when asked which candidate would best handle a major crisis.

Speaking from his hometown of Wilmington, Delaware, Mr Biden adopted a somber tone in a speech focusing on the coronavirus outbreak, calling for togetherness and praising doctors on the front line.