A young mum has allegedly been murdered by her partner in Mandurah, on Western Australia’s south-west coast.

Police said they found the 19-year-old woman with wounds to her throat and back after being called to the Aldgate Street home about 4pm (local time) yesterday.

Her partner, Junior Carlos, has been charged with murder and spent last night behind bars.

On his birthday Carlos, 26, was in court joined by his family, who were visibly upset as he sat in the dock dressed in a forensic suit.

Outside court the accused refused to answer questions from the media.

The victim, who had not been named, had only given birth to a baby girl six weeks ago. The child was not at home at the time of the alleged murder.

Neighbours told 9NEWS they did not see or hear anything yesterday, but did her screaming on the street the night before the teenager’s body was found.

Major Crime Detectives and Forensics spent the day scouring the house, trying to piece together the New Year's Eve tragedy.

The accused will stay behind bars until his next court appearance at the end of the month.

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