The incident, which police say did not involve any other vehicles, took place at around 1am on the busy A483 Carmarthen Road.
Police say the passenger sustained serious injuries as a result of the collision and the rider of the motorcycle made off on the bike prior to the arrival of the emergency services.
South Wales Police say they are appealing for any witnesses who may have any information or dash cam footage of the incident to contact them quoting reference number 2300368138.
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