The Senate Judiciary Committee has opened its confirmation hearing for Neil Gorsuch, President Donald Trump's US Supreme Court nominee, with Democrats questioning whether he would rule against abortion rights while favouring corporations.

The hearing on Monday comes 13 months after Justice Antonin Scalia's death created a vacancy on the Supreme Court. If Gorsuch is confirmed - which is widely expected - he would restore a 5-4 conservative court majority.

Republicans praised Gorsuch, a conservative federal appeals court judge from Colorado, as highly qualified for a lifetime appointment as a justice.

Democrats used their opening statements to question his record in ruling for business over its employees and his closeness to Trump.

Democratic Senator Richard Blumenthal underscored the importance of judicial independence at a time when Trump has excoriated federal judges who have ruled against him on matters including two executive orders, put on hold by courts, to block people from six Muslim-majority nations from entering the United States.

Blumenthal said it was not "idle speculation" to suggest the Supreme Court might be asked to enforce a subpoena against Trump, citing FBI Director James Comey's testimony before Congress on Monday confirming an ongoing investigation into alleged collusion between Trump's presidential campaign and Russia.

'Neutral and independent judges'

Gorsuch himself emphasised the need for "neutral and independent judges to apply the law," warned against judicial overreach, and referred to "the modest station we judges are meant to occupy in a democracy".

"If judges were just secret legislators, declaring not what the law is but what they would like it to be, the very idea of a government by the people and for the people would be at risk," Gorsuch said in comments in harmony with conservative criticism of unelected "activist judges".

Democrat Dianne Feinstein emphasised abortion. Conservatives have long opposed the landmark 1973 Roe v Wade ruling legalising abortion nationwide.

Feinstein called that ruling and others since then buttressing abortion rights "super precedents" deserving special deference.

A number of senators raised Gorsuch's ruling supporting a transportation firm that fired a driver for defying an order to stay in a freezing, broken-down truck

Questioning of Gorsuch will start on Tuesday and could go on for days.

Republican Chuck Grassley, the committee's chairman, said the panel is likely to vote on the nomination on April 3, with the full Senate vote likely soon after.

Democrats noted Gorsuch has the chance to join the court only because Senate Republicans last year refused to consider Democratic former president Barack Obama's nomination of federal appellate judge Merrick Garland.

They contend Trump's party "stole" a Supreme Court seat by freezing out Garland.

Several Senate Democrats have already announced plans to oppose Gorsuch and seek to block his nomination from coming to a final vote.

But delay tactics by Democrats could lead Senate Majority Leader Mitch McConnell to exercise procedural manoeuvres of his own to eliminate the 60-vote filibuster threshold now in place for Supreme Court nominations, and with it any Democratic leverage to influence the next Supreme Court fight.

Republicans control the Senate 52-48. The filibuster rule when invoked requires 60 of the 100 votes to advance a bill or nomination, contrasted with the simple 51-vote majority that applies in most cases.