US President-elect Joe Biden has said he will introduce an immigration legislation "immediately" after taking office, reversing the Trump administration's policies.

Biden will taken the oath of office on January 20.

"I will introduce an immigration bill immediately and have it sent to the appropriate committees to begin movement," he told reporters in Wilmington, Delaware on Friday.

Biden was responding to a question on what his administration would do first after his inauguration on January 20.

He had also previously promised an immigration overhaul within 100 days of taking office.

Reversing the Trump administration's "cruel" immigration policies was Biden's one of the key election promises.

Restricting immigration has been a focus of the Trump administration since its first days when it issued the travel ban on seven Muslim-majority countries, and it has continued into Trump's final year in office as the White House uses the coronavirus pandemic as cover.

The Trump government hardened the immigration rules on those allowed to seek asylum in the US and advocated a merit-based immigration system to protect US workers. His administration also tried ending the Deferred Action for Childhood Arrivals (DACA) in 2017, but the Supreme Court blocked its attempt in June 2019.

Biden said he will also countermand the Trump administration's orders on environmental issues.

"I will in fact, countermand the executive orders that the president has in fact initiated that are contrary to, what I think, is either his authority and/or even if it is his authority, contrary to the interest of the United States on environmental issues and a whole range of other things," he said.

Biden had vowed to rejoin the Paris climate agreement on the first day of his presidency. The US on November 4 last year formally withdrew from the 2015 Paris Agreement on Climate Change, a decision originally announced by President Donald Trump in 2017.

And thirdly, Biden said he will immediately move through to the most urgent need of asking the Congress to give him the financial wherewithal to deal with the coronavirus pandemic.

"To be able to move so that we have Operation Warp Speed really working. Warp Speed got the vaccine to places that were delivered but did not get them from those vials into people's arms and so it is a gigantic logistical concern of how we do that,” he said.

Biden said he is committed to get 100 million shots in people's arms in the first 100 days.

“I am committed to insisting that in all federal jurisdictions, any place I have control as president, everyone will be mandated to wear a mask interstate transportation as well as federal facilities.

"I am committed to moving as rapidly as possible to get the vaccine to teachers and the material to children that can provide for the safe opening of our schools at the end of that--beginning at the end of that 100 days. They are the most urgent things we have to do now. Now, immediately upon getting in office,” he said.

Biden said there is going to be multiple things and there will be other committees holding hearings on a whole range of issues on infrastructure, what they should be doing to generate a green economy.

"But in terms of the immediate need to get done not just introduced but to get done, voted on and get the money and resources to do it turns out that the most urgent need is dealing with the virus number one and economic relief to Americans who through no fault of their own are really getting battered,” he said.