A small group of hard-left activists burned foot-long United States (US) flags outside the Trump International Hotel in New York on Tuesday, in an angry response to a tweet by president-elect Donald Trump that flag-burners should face legal consequences.

Social media was itself ablaze on Tuesday in response to Trump's tweet that read: "Nobody should be allowed to burn the American flag ─ if they do, there must be consequences ─ perhaps loss of citizenship or year in jail!".

Trump's provocative tweets on flag-burning and other topics, including efforts to recount the Nov 8 presidential vote, came as the Republican worked to fill his Cabinet in advance of his inauguration in January.

The US Supreme Court ruled in 1989 that flag-burning was not a crime but rather a form of protest protected by the First Amendment of the Constitution. The high court has also ruled more than once that citizenship cannot be revoked.

US media outlets, including the New York Times, published articles detailing the court rulings, and some Republicans as well as Democrats took to social media to say Trump was in effect threatening to punish dissent despite constitutional protections.

Trump supporters also took to social media, pointing out that many politicians, including Trump's Democratic presidential rival, Hillary Clinton, had proposed making flag-burning illegal.

Clinton, while a US senator, co-sponsored a 2005 bill that would have made it a crime to incite violence by burning a flag, threaten another person with a burning flag or destroy or damage a flag belonging to someone else. The measure failed.

Tuesday's protest in New York involved seven members of the Revolutionary Communist Party, a group that is not affiliated with the Communist Party of the United States, and whose members participated in flag-burning at the Republican National Convention in Cleveland in July.