Joe Biden won the endorsement for US president Monday of Nancy Pelosi, who hailed him as a "voice of reason" capable of leading America out of the coronavirus crisis.

Pelosi was the last leading Democrat to endorse formally Biden's run for the White House against Republican Donald Trump in November.

Biden, who served as vice president under former president Barack Obama, had already emerged as the Democrats' presumptive nominee after decisive primary victories in a string of primaries before the COVID-19 pandemic shut down much of the country.

His main rivals, including Vermont Senator Bernie Sanders, have dropped out of the race and endorsed Biden as has Obama.

In her statement, Pelosi lauded the former senator from Delaware as a man of "empathy, grace and courage" and "a leader with the humility to seek expertise in science and the confidence to act on it."

"As we face coronavirus Joe Biden has been a voice of reason and resilience with a clear path to lead us out of this crisis," she said.