One of Sean 'Diddy' Combs' former employees has testified that the hip-hop mogul kidnapped her at gunpoint, then broke into rapper Kid Cudi's home in a plot to kill his love rival.

Capricorn Clark, who worked on and off for Mr Combs for more than a decade, told his trial that the defendant and a security guard had shown up at her apartment in 2011 and forced her to drive with them to Kid Cudi's home.

"Get dressed," she recalled Mr Combs saying. "We're going to go kill this [expletive]." She also told the court Diddy had threatened to kill her on her very first day working for him.

Mr Combs, 55, has pleaded not guilty to racketeering, sex trafficking and transportation to engage in prostitution.

The Kid Cudi incident was first discussed in the trial last week when that rapper, whose legal name is Scott Mescudi, took the stand to testify against Mr Combs.

He detailed his relationship with Mr Combs' ex-girlfriend, Cassie Ventura, an alleged break-in at his Los Angeles home and an incident in which his Porsche was damaged by a Molotov cocktail, which he believed Mr Combs orchestrated.

Mr Combs is facing possible life in prison if convicted on federal charges of racketeering, sex trafficking and transportation to engage in prostitution.

The rapper has separately denied accusations in a barrage of civil lawsuits that echo some of the claims made in his criminal case.

In her testimony on Tuesday, Ms Clark - who was global brand director for Mr Combs' Bad Boy Entertainment - said the hip-hop mogul had arrived at her home in 2011 after he discovered Ms Ventura was in a relationship with Mr Mescudi.

Mr Combs was holding a gun in his hand when he arrived, she said, and appeared "livid" and told her "we're going to kill" Mr Mescudi.

She told the court he forced her to get into a car and go with them against her will, the BBC's US partner CBS News reported.

Under cross-examination by Mr Combs' lawyer, Ms Clark denied that she went with him voluntarily.

Once they arrived at Mr Mescudi's home, Mr Combs and a security guard went inside while she called Ms Ventura from the car and told her what was unfolding.

When Mr Combs returned and caught her on the phone, he became more angry, Ms Clark said, adding that they sped off as Mr Mescudi arrived back at his home.

Afterwards, the court heard that the defendant had told Ms Clark he would not let her go until she and Ms Ventura persuaded Mr Mescudi that Mr Combs was not involved in the break-in at his LA home.

"If you don't convince him of that, I'll kill all of you," Mr Combs told Ms Clark, she testified.

Ms Clark also described the difficult working relationship she had with Mr Combs over the years.

On her very first day in the job, she testified, Mr Combs threatened to kill her as he warned that her past work for other rappers had better not become a problem for him.

But, she told the court, despite the tumult, she also felt like his protector and wanted to remain in his circle.

"He broke the ceiling of what we were allowed to do as black people in the business world."