Tributes poured in for former astronaut and US senator John Glenn, the first American to orbit the Earth, who died yesterday at age 95.

US President Barack Obama, who was less than a year old when Glenn made his storied flight in 1962, said Glenn taught Americans "that with courage and a spirit of discovery there's no limit to the heights we can reach together".

Obama said Glenn "always had the right stuff," a reference to Tom Wolfe's 1979 book The Right Stuff about the first class of US astronauts, which was made into a Hollywood movie in 1983.

"The last of America's first astronauts has left us, but, propelled by their example, we know that our future here on Earth compels us to keep reaching for the heavens," Obama said.

President-elect Donald Trump said the US "lost a great pioneer of air and space." He said Glenn "was a hero and inspired generations of future explorers. He will be missed".

Glenn, who parlayed his space-flight fame into a political career in which he served four terms in the US Senate, died after being admitted to hospital in Columbus, Ohio, not far from his hometown.

No cause of death was given, but he had suffered a stroke and undergone heart surgery in recent years, according to news reports.

Ohio Governor John Kasich announced Glenn's death on Twitter, saying, "John Glenn is, and always will be, Ohio's ultimate hometown hero, and his passing today is an occasion for all of us to grieve."

The National Aeronautics and Space Administration (Nasa) also reacted to Glenn's death on Twitter, calling him "a true American hero.

Chosen in 1959 as one of the seven original astronauts, Glenn was the last member of the so-called Mercury Seven to die.

Glenn made his historic orbit around the Earth on Feb 20, 1962, during the height of the Cold War and as the US and the Soviet Union were racing to become the first to land astronauts on the moon.

Glenn flew solo on the Mercury-Atlas 6 mission, circling the globe three times during a flight that lasted nearly five hours.

Clad in a silver metallic space suit common in the era, Glenn, who was 40 at the time, was the third American in space.

Problems with the new Atlas rocket and poor weather forced several postponements of the mission, raising anxiety levels among Nasa engineers.

The flight engineer who initiated the launch sequence also uttered a prayer, to which astronaut Scott Carpenter added the words, "Godspeed, John Glenn."

Glenn's aviation career began in 1942 when he joined the Marines and became a pilot. He served in World War II and the Korean War before joining Nasa.

Glenn won the Senate seat in 1974, as a Democrat representing the Midwestern state of Ohio, and went on to serve four consecutive terms. He made a bid for president in 1984, but failed to win the nomination.

In 1998, the year before his retirement from politics, Glenn became the oldest person to fly in space at age 77.

Glenn's flight aboard space shuttle Discovery was designed to help scientists learn about the effects of conditions in space on older people.

- dpa