US comedian Chris Rock has been criticised for a joke he made while hosting the Oscars ceremony, at the expense of Asian-Americans.

Activists accused him of perpetuating racial stereotypes when he introduced a group of accountants, who turned out to be three Asian children in suits.

Chris Rock has been generally praised for the way he dealt with the absence of black artists among Oscar nominees.

The ceremony had been boycotted by some Hollywood figures.

All 20 nominees in the best acting or supporting acting categories were white.

Chris Rock had addressed the controversy during his hosting of Sunday night's Academy Awards show, commenting that he had "counted at least 15 black people" in the montage that opened the ceremony, before welcoming people to the "white People's Choice awards".

The skit involving the three children was an apparent reference to Asians being good at maths. One of the children was also given a Jewish surname.

Rock then said: "If anybody is upset about that joke, just tweet about it on your phone, which was also made by these kids."

Critics say the punch line was another stereotype, about child labour in Asia.

Actress Constance Wu tweeted: "To parade little kids on stage w/no speaking lines merely to be the butt of a racist joke is reductive & gross. Antithesis of progress."

Mee Moua, who heads the group Asian Americans Advancing Justice, said in a statement that the show was a setback for diversity.

"Last night's ceremony, and particularly the 'joke' involving Asian children, which played off more than one damaging stereotype of Asians and Asian Americans, exposed one of the failings of how we talk about race in America: race relations are not a black-white binary," she said.

"It is to all of our detriment to look at race narrowly. We need to work together to dismantle the systems that devalue the experiences of minority groups so we can see the tales of the diversity that have shaped our nation reflected accurately."

Rock's publicist Leslie Sloane said on Monday that the star was unavailable for comment.

The Academy of Motion Picture Arts and Sciences also did not respond to a request for comment.