Players and coaches took a knee during the US national anthem as the NBA season restarted at Disney World in Florida on Thursday.

Players from the Utah Jazz and New Orleans Pelicans wearing t-shirts bearing the slogan "Black Lives Matter" kneeled in unison just before tip-off as the "Star-Spangled Banner" played.

Thursday's restart in Orlando is taking place four months after the league shut down in March due to the coronavirus pandemic.

The resumption of the NBA follows a period of soul-searching about racism and police brutality in the United States following the death of unarmed black man George Floyd during his arrest by police on May 25 in Minneapolis.

Many NBA players joined protests against the killing which swept across all 50 states in June, and the cause of social justice has loomed large ahead of the league restart.

Large "Black Lives Matter" slogans have been written on each court, while players are allowed to wear jerseys adorned with social justice messages ranging from "I Can't Breathe" to "Justice Now" and "Education Reform."

Taking a knee has become an emblematic way of showing support for the Black Lives Matter movement, adopted by athletes around the world in the months since Floyd's death.

Kneeling during the US national anthem was first started by former San Francisco 49ers quarterback Colin Kaepernick in 2016.

Kaepernick used the gesture to draw attention to racial injustice after the deaths of several African-Americans at the hands of law enforcement.

The 49ers quarterback was widely vilified for his stance and has not played in the NFL since being released by San Francisco in early 2017.

The NBA had had a longstanding rule requiring players to stand for the national anthem before games.

But NBA Commissioner Adam Silver hinted on Thursday that players were unlikely to be sanctioned for kneeling, citing the "unique moment" of the recent protests.

"We've had a rule in place for a long time that requires players to stand," Silver told CNN. "I will say though that I do respect peaceful protest. We'll see what happens if (they kneel).

"But I understand this is a unique moment in our history."

The NBA is relaunching its season with 22 teams based in a secure zone at the ESPN Wide World of Sports Complex inside the sprawling Disney World resort.

Utah's game against New Orleans will be followed later Thursday by a heavyweight showdown between the Los Angeles Lakers and Los Angeles Clippers.

Thursday's games marked a resumption of regular season play to determine the final line-up for the NBA playoffs, which start on August 17.

Utah's Rudy Gobert -- the first NBA player to be infected with COVID-19 whose case triggered the league's shutdown -- was back in the line-up for the Jazz on Thursday.

The tightly-controlled "bubble" setting in Orlando is designed to prevent an outbreak of COVID-19 halting play once more.

Players in the bubble are required to undergo regular COVID-19 testing and the ability to enter and exit the secure zone is subject to stringent regulations.

Team and NBA personnel are staying in three hotels dotted throughout the resort, with a small number of media, sponsors and inactive players also allowed in.

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