Two former Michael Jackson employees have painted a lurid picture of the pop star's behaviour at Neverland Valley Ranch, testifying he had oral sex with a young boy at midnight and secret kisses with Home Alone star Macaulay Culkin.

Former Neverland security guard Ralph Chacon told jurors on Thursday that he watched through a bathroom window late one night in the early 1990s as Jackson fondled and kissed a boy who later collected a reported $23 million (12.3 million pounds) from the entertainer in an out-of-court settlement.

"I saw them standing in the nude ... facing each other. I saw that Mr Jackson was caressing the boy's hair, kissing him on his head, his face, his lips," said Chacon, whom a defence lawyer suggested was nursing a grudge after losing a $1.4 million lawsuit to the singer.

"(Jackson) started sucking his nipples, started going down to his penis," Chacon said. "He put the little boy's penis in his mouth."

Chacon, who said he had earlier seen the pair showering together, described a separate incident in which Jackson planted a "passionate" kiss on the boy's mouth and placed his hands on the youth's crotch while they stood before a Peter Pan and Tinkerbell display.

During a blistering cross-examination by Jackson attorney Tom Mesereau, Chacon conceded that he was ordered to pay Jackson $1.4 million in the wrongful termination suit after a judge found that he had stolen from the pop star.

Jackson's mother, Katherine, and brother Tito, walked out of court during Chacon's testimony.

Onetime Neverland maid Adrian McManus described Jackson kissing three boys who routinely shared his bed, including the youth identified by Chacon in the bathroom incident. McManus said she was "shocked" to see Jackson's hand on the boy's privates.

She was also concerned about Jackson's behaviour toward Culkin, once stumbling on what she said was a disturbing scene as she walked out of his bathroom.

"I saw Mr Jackson and Macaulay in the library and Mr Jackson was kissing him on his cheek and he had his hand kind of on his leg, kind of on his rear end," McManus said.

The housekeeper, who told of a similar kissing incident between Jackson and a third boy, said she frequently found underwear belonging to Culkin and the other boys in or near the singer's spa bath.

Representatives for Culkin, who has denied that Jackson ever acted inappropriately, say he won't testify in the case.

Jackson is charged with molesting a 13-year-old boy, plying the youth with alcohol in order to abuse him and conspiring to commit child abduction, extortion and false imprisonment. The 46-year-old singer, who has pleaded innocent, faces more than 20 years in prison if convicted.

Both McManus and Chacon were involved in the failed lawsuit against Jackson after leaving their Neverland jobs. The suit resulted in a six-month trial in which a judge found that they had acted with "fraud, oppression and malice" and stole from the pop icon.

"After a six-month trial this is a good way to get even with (Jackson), isn't it?" Mesereau asked Chacon. Prosecutors objected to the question and Chacon was not allowed to answer.

Chacon and McManus, who admitted selling their story to tabloid newspapers, said they sued Jackson because they were forced out amid the 1993 sex abuse accusations against him.

Both claimed they had been harassed and threatened by members of Jackson's armed personal security detail. Chacon said an anonymous phone caller threatened to kill him and McManus told of being chased by a Jackson bodyguard wielding a stun gun.

McManus said she lied during a deposition in the 1993 case when she denied any improper behaviour by Jackson. She did so because Jackson once threatened that someone would "come after her" if she ever did anything wrong, she said.