Democrats protested President Donald Trump's address to Congress on Tuesday with signs reading "No King!" and "Save Medicaid," with some turning their backs on the Republican as he spoke and one lawmaker marched out by security.

Representative Al Green of Texas, a Democrat who plans to introduce articles of impeachment against Trump, loudly interrupted the speech in its first minutes by shouting that Trump did not have a mandate to cut safety net programmes.

Republicans are trying to pass a spending bill that could significantly slash spending on popular social programs, including the Medicaid health insurance plan for low-income people, to pay for Trump's desired tax cut plan.

House Speaker Mike Johnson ordered the sergeant-at-arms to remove Green from the chamber, and Republicans cheered as Green relented - waving his cane in the air - and was led out.

Green told reporters afterward, "It's worth it to let people know that there are some of us who are going to stand up against this president's desire to cut Medicaid, Medicare and Social Security."

With Republicans holding majorities in the House of Representatives and Senate, any impeachment effort against Trump is unlikely to advance.

Around a third of the Democrats' side of the chamber had emptied as Trump's address crossed the threshold to become the longest such speech on record at an hour and 30 minutes. The rest quickly departed as Republicans gave Trump a standing ovation when the speech ended after 100 minutes, the longest in Congressional history. (Reuters)