A 32-year-old man with an intellectual disability won an appeal on Wednesday against his eight-month prison term for possessing a petrol bomb and a laser pointer, with a judge ordering his immediate release.

Lee Kai-fat, who has the IQ of an 11-year-old, was arrested at a Light Rail stop in Tuen Mun in January after a petrol bomb attack on the police station in the area.

Lee, who worked as a cleaner, pleaded guilty to possessing offensive weapons and was jailed in June.

But the High Court heard how the magistrate in the case had failed to take into account Lee's intellectual disability.

The judge ruled in Lee's favour and ordered his immediate release, saying he had already served more than four months behind bars and keeping him there any longer could affect his rehabilitation.

The judge, Alex Lee, said he would provide more detailed reasons for his decision at a later date.