WASHINGTON - US President Joe Biden signed a slew of executive orders to combat the coronavirus, tackle climate change and reverse his predecessor Donald Trump's immigration policies on his first day in office.

He also signed orders to start the process of rejoining the World Health Organisation (WHO) and Paris Climate Agreement, signalling his commitment that America would once again embrace international institutions and be a global leader.

Mr Biden has written to the United Nations' Secretary-General stating that the United States intends to remain a member of the WHO, according to the White House.

"His priority is first rebuilding our partnerships and alliances around the world, and regaining America's seat at the global table," said White House press secretary Jen Psaki at her first press briefing on Wednesday (Jan 20), in response to a question on Mr Biden's global priorities.

She added: "You can see that as evidenced in his rejoining the Paris Climate Agreement, rejoining the World Health Organisation, his plans to engage with partners and allies and work together to address many of the threats and issues we're facing around the world."

Mr Biden dove head first into tackling the four "converging crises" of the pandemic, the economic downturn it caused, climate change and racial injustice.

Though he will focus primarily on domestic issues in his first days in office, the President has acknowledged that tackling the pandemic and climate change in particular will require global cooperation.

His first phone calls with foreign leaders will be with allies and partners, said Ms Psaki, adding that Canadian Prime Minister Justin Trudeau is first in line on Friday.

"With the state of the nation today, there's no time to waste," said Mr Biden in the Oval Office, following a scaled down inaugural parade in Washington after he took his oath of office at the Capitol.

"Some of the executive actions I'm going to be signing today are going to help change the course of the Covid crisis. And we're going to combat climate change in a way that we haven't done so far, and advance racial equity and support other under-served communities," he told reporters.

Wednesday's executive actions were just "starting points", said Mr Biden, adding that legislation would also be needed for a lot of his policies.

Mr Biden signed an order requiring masks to be worn on federal property, and asked agencies to provide relief to Americans hit by the pandemic by extending the pauses on evictions and foreclosures and federal student loan payments.

He also officially appointed a Covid-19 response coordinator to create a unified national response to the pandemic, and re-established the national security team responsible for global health security and biodefence.

He cancelled the permit for the Keystone XL pipeline that would have transported crude oil from Canada to the US, among other actions to strengthen environmental protections.

On immigration, he signed orders to halt construction of the US-Mexico border wall and to reverse Mr Trump's travel ban for Muslim-majority countries.

The new administration will also pause some deportations for 100 days to ensure "fair and effective immigration enforcement" and focus on US-Mexico border security, a Department of Homeland Security memo issued late on Wednesday said.

Mr Biden also sent an immigration reform Bill to Congress, titled US Citizenship Act Of 2021, that would provide undocumented immigrants who have lived in the US for a long time with an eight-year path to citizenship.

Mr Biden also signed an order to advance racial equity and root out systemic racism from federal programmes and institutions.

The President planned to sign a total of 17 executive orders and memorandums on Wednesday, far more than his recent predecessors, US media reported. Mr Trump signed one executive order on his first day in office, and Mr Barack Obama signed none.

But Mr Biden is also running behind in terms of Cabinet-level posts. Only one of his nominees has been confirmed by the Senate, which had been slow to schedule hearings in the wake of Mr Trump's insistent false claims that the election was rigged against him, and because control of the Senate was decided only on Jan 5.

Director of National Intelligence Avril Haines was confirmed on Wednesday night by a vote of 84 to 10.

In contrast, Mr Trump had two Cabinet posts filled by the time he took office, while Mr Obama had six.

The White House announced on Wednesday that it was appointing career public servants to temporarily lead their agencies while Mr Biden's picks await Senate confirmation.

Over at the Capitol, Vice-President Kamala Harris swore in three new Democratic senators: her successor Alex Padilla, who was appointed to fill the California seat she vacated after winning the 2020 election, and Georgia Democrats Raphael Warnock and Jon Ossoff.

Mr Warnock's and Mr Ossoff's victories in this month's run-off races handed de facto control of the Senate to the Democratic Party for the first time in a decade.

Republicans and Democrats now have 50 senators each, but Ms Harris, who is the president of the Senate, will get to cast the deciding vote in case of any ties.