A woman has been jailed after allegedly breaking into her ex-boyfriend's house then forcing him to have sex with her at machete-point.

Montana police say Samantha Ray Mears forced her way into her former partner's home and hid behind his bedroom door while he was away, the Great Falls Tribune reports.

When he returned home, the 19-year-old brandished her machete and ordered him to remove his clothing.

The man complied out of fear, after which Ms Mears allegedly took her pants off and proceeded to have sex with him with machete still in hand.

The ex-boyfriend told police he attempted to push her away but claims Ms Mears bit him.

Ms Mears then allegedly sat on the bed with her back to the wall and began arguing with her ex following the sex act.

He also accused her of damaging his wall and urinating on his bed.

The man told Ms Mears he was going to call someone by the name of "Doug" and left the room, dialling 911 instead.

Ms Mears reportedly fled the scene just as police arrived but was arrested shortly afterwards.

Ms Mears has since been charged with aggravated burglary, assault with a weapon, unlawful restraint, partner family member assault and two counts of criminal mischief.

Ms Mears told police a different story, claiming her ex kidnapped then armed her with the machete.

In April, she was charged with felony strangulation for allegedly assaulting the same victim.

Police suspect Ms Mears may be suffering from mental illness.

Ms Mears and her alleged victim were in a relationship for about seven years, court documents show.