WASHINGTON: Justice Antonin Scalia, a towering conservative voice on the United States (US) Supreme Court, has died at the age of 79, setting up a political showdown over his succession in the run-up to the presidential election.

His death after three decades on the Supreme Court bench, coming 11 months before a new American president takes office, could potentially tip the balance of the highest court in the land from its current 5-4 conservative majority to a liberal one.

The flag outside the Supreme Court was lowered to half-staff in tribute to Scalia, who died in his sleep at a private residence in the Big Bend area of West Texas, according to the US Marshals Service.

President Barack Obama led tributes for the court's longest-serving justice, who was first appointed in 1986 by Ronald Reagan.

"For almost 30 years, Justice Antonin Scalia was a larger than life presence on the bench, a brilliant legal mind with an energetic style," Obama told reporters in Rancho Mirage, California.

"Tonight we honor his extraordinary service to our nation and remember one of the towering legal figures of our time."

Obama also made clear he fully intended to nominate a successor to Scalia, in accordance with his "constitutional responsibilities", after leading Republicans demanded the task be left to the next president.

He called for the Republican-controlled Senate to give his nominee a "fair hearing and a timely vote". "These are responsibilities that I take seriously as should everyone," Obama added. "They're bigger than any one party. They are about our democracy."

The president nominates a Supreme Court candidate, who requires Senate approval before taking up the lifetime post.

Court's future in play

For three decades, Scalia's outsized personality gave voice to the values of conservative America on the Supreme Court bench, on matters of religion, family, patriotism and law enforcement.

A staunch defender of the death penalty and the individual right to bear arms, the Roman Catholic justice was also openly opposed to abortion, gay marriage and affirmative action.

The Supreme Court's conservative majority had recently stalled key efforts by Obama's administration on climate change and immigration.

But replacing Scalia with a Democratic appointee could significantly alter the balance of the court.

Republicans immediately drew battles lines over the implications of the vacancy, which former senior Obama advisor David Axelrod described as a "seismic event" that will have a major impact on the presidential race.

"The American people should have a voice in the selection of their next Supreme Court Justice," said Senate Republican Majority Leader Mitch McConnell. "Therefore, this vacancy should not be filled until we have a new president."

But leaving the nomination to the next head of state, who will not be sworn until January 2017, would mean the court is short-handed for a year or more.

Senator Chuck Grassley, Chairman of the Senate Judiciary Committee, also issued a statement calling for a delay in the nomination.

"It's been standard practice over the last 80 years to not confirm Supreme Court nominees during a presidential election year," he said.

'Shameful abdication'

The Republican calls met with a sharp rebuttal from the Democratic camp.

McConnell's Democratic counterpart Harry Reid pressed for Obama to send a nominee to the Senate "right away", stressing that a yearlong vacancy would be “unprecedented. “

"Failing to fill this vacancy would be a shameful abdication of one of the Senate's most essential Constitutional responsibilities," Reid said.

Democratic White House hopeful Hillary Clinton said Republicans calling for a delay "dishonour our Constitution."

'Towering figure'

The often belligerent Scalia, the first Italian-American to serve on the Supreme Court, was known for his brash demeanor and sharp tongue.

He once referred to a "junior-varsity Congress". "War is war and it has never been the case that when you capture a combatant, you have to give them a jury trial in your civil courts," he said, referring to prisoners at the US military prison at Guantanamo Bay. "It's a crazy idea to me."

Obama's Republican predecessor George W. Bush mourned the passing of a "towering figure". "He brought intellect, good judgment and wit to the bench, and he will be missed by his colleagues and our country," Bush added.

Chief Justice John Roberts mourned Scalia's passing as a "great loss to the court and to the country he so loyally served."

Republican presidential frontrunner Donald Trump hailed Scalia as "one of the best of all time". "His career was defined by his reverence for the Constitution and his legacy of protecting Americans' most cherished freedoms,”" Trump added.

"He was a justice who did not believe in legislating from the bench and he is a person whom I held in the highest regard and will always greatly respect his intelligence and conviction to uphold the Constitution of our country."