Las Vegas police have launched a homicide investigation into the death of BB King, a Nevada coroner's office says, after the blues guitar legend's daughters reportedly accused his aides of poisoning him.

King died at age 89 on May 14 in Las Vegas, where he kept his residence while he maintained a gruelling schedule of tours that ended only last year.

Two of King's daughters — Karen Williams and Patty King — have alleged he was poisoned by his business manager Laverne Toney and his personal assistant.

"I believe my father was poisoned and that he was administrated foreign substances to induce his premature death," the daughters wrote in separate but identical affidavits published by entertainment site Eonline.

"[I] request a formal investigation into this matter," the court documents said.

Ms Toney, who is the executor of King's estate, shrugged off the daughters' charge.

"They've been making allegations all along. What's new?" Ms Toney said, according to Eonline's report.

The Clark County, Nevada, coroner's office said on Twitter that it had taken jurisdiction of King's body and would perform an autopsy, with the results to be finalised after a minimum of six weeks.

The Las Vegas police department would investigate the possibility of homicide, the tweet said.

An attorney for King's estate also dismissed the daughters' accusations as "ridiculous".

"I hope they have a factual basis that they can demonstrate for their defamatory and libellous allegations," Brent Bryson said in a statement.

Autopsy results won't be known for at least six weeks: coroner

The Las Vegas police department would investigate the possibility of homicide, the tweet said.

Given the timeframe for the autopsy, King's funeral in his beloved Memphis has been postponed, local media reported.

Riley B King was born in poverty and grew up working in cotton fields, but went on to master the guitar and entered the music business after travelling to Memphis and working for radio stations.

He became known as the Beale Street Blues Boy, which eventually earned him the moniker BB King.

For decades, King played shows almost every night, becoming the premier ambassador for the blues — the music genre that emerged from African American spirituals in the Deep South.

In Memphis, his longtime place of residence, the BB King Museum and Delta Interpretive Centre opened in 2008 to showcase artefacts from the legendary guitarist, as well as the cultural heritage of the Mississippi Delta.

His final resting place could turn the museum into even more of a tourist draw.

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AFP