A couple who were allegedly murdered by their son and one of his friends were dismembered and cooked in a microwave oven, a court in Hong Kong has heard.

Prosecutors say Henry Chau Hoi-leung, 30, killed his 63-year-old mother Siu Yuet-yee and 64-year-old father Chau Wing-ki, with the help of an accomplice identified as Tse Chun-kei, 36.

Police found the heads of the couple inside a fridge in a flat in the Tai Kwok Tsui district in March last year.

Chau and Tse pleaded not guilty to murder at the first hearing of their trial in the former British colony, the South China Morning Post reported.

Prosecutor Michael Arthur told the court that the pair had been planning the killing for months.

Chau and Tse allegedly bought two microwave ovens, a rice cooker and a number of knives in preparation for their gruesome plan, up to three months before luring Chau's parents to the flat with an excuse.

The court heard that the victims' dismembered bodies were found as police raided the flat after Chau told detectives investigating his parents' disappearance that they had crossed to the Chinese mainland for a pleasure trip. Police had found no record of them leaving Hong Kong.

Beside the married couple's heads, authorities found other body parts stored in bags and boxes at the premises. The court heard that some had been salted and microwaved, The Standard reported.

The trial continues.