Barack Obama, Billie Jean King and LeBron James led rallying calls on a seismic day in American sport, as games were called off in protest at racial injustice.

In a forceful message, athletes and teams downed tools in North America as they boycotted scheduled fixtures following the shooting of Jacob Blake, a black man, by police in the state of Wisconsin.

Blake was shot several times in the back, prompting nationwide protests.

All three NBA playoff games set for Wednesday were postponed, and it was reported widely that players from the Los Angeles Clippers and the Los Angeles Lakers were in favour of boycotting the rest of the season.

The NBA board of governors were set for a Thursday meeting, with players also reportedly due to hold a follow-up to their Wednesday get-together.

Major League Baseball saw three games postponed, namely those between the Milwaukee Brewers and Cincinnati Reds, Los Angeles Dodgers and San Francisco Giants, and Seattle Mariners and San Diego Padres.

Five of six Major League Soccer games also did not go ahead, while Thursday's play at the Western and Southern Open tennis tournament in New York was suspended, with Naomi Osaka pulling out of the tournament after reaching the semi-finals.

Former US president Obama saluted the Milwaukee Bucks for boycotting Game 5 in their series against the Orlando Magic.

Milwaukee is the nearest major city to Kenosha, where Blake was shot. Obama also saluted Clippers coach Doc Rivers, who criticised President Donald Trump when he spoke powerfully on Tuesday. Rivers accused the Republican Party of "spewing this fear".

Obama wrote on Twitter: "I commend the players on the @Bucks for standing up for what they believe in, coaches like @DocRivers, and the @NBA and @WNBA for setting an example. It's going to take all our institutions to stand up for our values."

Speaking earlier in the day, Lakers superstar James wrote on Twitter: "F*** THIS MAN!!!! WE DEMAND CHANGE. SICK OF IT".

Clippers owner Steve Ballmer added: "I am again angry over the shooting of a black man #JacobBlake. @DocRivers and The @Bucks players said it well, we need real police accountability. Give citizens data to do so. Let's have criminal justice reform that keeps all people safe but not senselessly imprisoned or afraid."

Tennis great King, who has fought for the growth of women's sport and for social justice, praised Japanese player Osaka's decision to abandon the Western and Southern Open in her individual protest.

King wrote: "A brave and impactful move by @naomiosaka, in support of the protest movement moving through the sports world. She was to play in the semis. Athletes using platforms for good means so much. Don't remain silent. #BlackLivesMatter"

Fellow tennis Hall of Famer Martina Navratilova added: "An amazing stance Naomi ... well done, nothing but respect!!!"

The NHL faced criticism, however, for a perceived lack of response as the Stanley Cup playoffs continue.

Canadian star Evander Kane, who plays for the San Jose Sharks, tore into the league by saying: "Actually it's incredibly insulting as a black man in hockey the lack of action and acknowledgement from the @nhl, just straight up insulting."