Known for his roles in the Christmas film Elf and US sitcom The Big Bang Theory, Newhart also had his own programme, The Bob Newhart Show.

Jerry Digney, Newhart's publicist, said Newhart had died at the age of 94 after "a series of short illnesses".

Newhart launched his career as a stand-up comic in the late 1950s.

He gained nationwide fame in the US when his routine was captured on vinyl in 1960 as The Button-Down Mind of Bob Newhart, which went on to win a Grammy Award as album of the year.

Read more:
Man fined after being caught with a salmon up his sleeve
If Joe Biden steps aside, who could replace him?

Newhart also won as best new artist of 1960, and the sequel The Button-Down Mind Strikes Back! won as best comedy spoken word album.

Over the years, Newhart also appeared in several movies, usually in comedic roles.

They included Catch 22, In And Out, Legally Blonde 2 and Elf, as the diminutive dad of adopted full-size son Will Ferrell.

More recent work included Horrible Bosses and the TV series The Librarians, as well as The Big Bang Theory and its spin-off series, Young Sheldon.

His sitcoms, nominated several times for an Emmy, included Bob, and George & Leo.

"I guess they think I'm not acting. That it's just Bob being Bob," he said of his failure to win an Emmy.

Newhart continued appearing on television occasionally after his fourth sitcom ended and vowed in 2003 that he would work as long as he could.

"It's been so much, 43 years of my life; [to quit] would be like something was missing," he said.