US President Joe Biden has begun to undo some of Donald Trump's key policies, hours after being sworn in.

"There is no time to waste when it comes to tackling the crises we face," he tweeted as he headed to the White House following his inauguration, according to the BBC.

President Biden reportedly signed 15 executive orders, firstly to boost the federal response to the coronavirus crisis.

A series of measures will be enacted to tackle the coronavirus pandemic which has claimed more than 400,000 lives in the United States.  There will be a mandate to wear masks and practice social distancing on all federal government property.

Mr. Biden has also pledged to make the fight against climate change a top priority of his administration.

He signed an executive order beginning the process of rejoining the 2015 Paris climate agreement, from which Mr. Trump formally withdrew the US last year.

Mr. Biden has also revoked the presidential permit granted to the controversial Keystone XL Pipeline, which environmentalists and Native American groups have fought for more than a decade.

Other orders reverse the Trump administration's stance on climate change and immigration.

According to Metro, one of the most notable Trump decrees reversed by Biden was the former president’s so-called Muslim ban, which barred travelers from seven Muslim-majority countries from entering the US. He also wants to distribute 100million doses of coronavirus vaccines during his first 100 days in office, and help offer better healthcare to Americans living in poverty.

Trump signed the Muslim ban shortly after coming into office in January 2017, and said he had done so for national security reasons.