Police in Las Vegas have begun a murder investigation into the death of BB King after the blues guitar legend's daughters reportedly accused his aides of poisoning him.

King died aged 89 on 14 May in Las Vegas, where he lived while he kept up a touring schedule that ended only last year.

Two of his 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 reportedly wrote in separate but identical affidavits.

The court documents reportedly called for a formal investigation, according to the Eonline website.

Ms Toney, who is the executor of King's estate, said: "They've been making allegations all along. What's new?".

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.

Earlier the local coroner confirmed the murder investigation and said a post-mortem examination would be carried out on King's remains.

Given the timeframe for the post mortem, King's funeral in 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 Center 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.

Elvis Presley was buried at his Graceland estate, which draws 500,000 visitors a year and is by far the biggest tourist attraction in Memphis.