Former US Vice President Joe Biden officially won the Democratic Party's presidential nomination after a virtual roll call vote at the party's national convention, during which a lineup of speakers hammered President Donald Trump on leadership.

Biden secured 3,558 delegates after the roll call vote on Tuesday, which took place at a largely virtual convention, which was nominally held in Milwaukee, Wisconsin. Candidates needed 1,991 delegates to win the presidential nominee for their party, a threshold Biden reached earlier on after Senator Bernie Sanders dropped out.

The second night of the four-day virtual Democratic National Convention was themed on leadership, especially on a global scale, and Democrats took the opportunity to criticize Trump's foreign policy.

Former Secretary of State John Kerry in his remarks said Trump is incapable of defending the country in contrast to Biden's "steady" hand.

Kerry said Joe Biden can make "America lead like America again." "This moment is a fight for the security of America and the world," the Obama administration's top diplomat added.

Former Secretary of State Colin Powell, who served under the George W. Bush administration, also made a case for supporting Biden. Powell said Biden will stand up to adversaries and trust US diplomats and the intelligence community.

US Senate Minority Leader Chuck Schumer said the United States needs a "steady" US president to pull the country out of its crisis.

Former President Bill Clinton slammed Trump for his mishandling of the US response to the domestic outbreak of the novel coronavirus disease (COVID-19) and his disagreement with advice from medical experts.

"COVID hit us much harder than it had to," Clinton claimed.

Former President Jimmy Carter also spoke in support of Biden. The Democrats' presumptive vice presidential nominee, Senator Kamala Harris, will be the keynote speaker on Wednesday, the night before Biden delivers his nomination acceptance speech from Delaware.

The Republican National Convention is scheduled to take place August 21-24 at Charlotte, North Carolina. Trump said he will deliver his acceptance speech from the White House lawn.