A Minnesota judge has ruled that six siblings of pop music superstar Prince are the heirs to his vast estate, more than a year after his death from an accidental drug overdose, according to court documents just released.

Prince's sister, Tyka Nelson, and his half siblings, Omarr Baker, Alfred Jackson, Sharon Nelson, Norrine Nelson and John Nelson, were designated as the musician's heirs by Carver County District Judge Kevin Eide.

Prince died at age 57 of an accidental, self-administered overdose of the powerful painkiller fentanyl in April 2016 a this Paisley Park Studios compound in the Minneapolis suburb of Chanhassen.

The creator of hits such as Purple Rain and When DovesCry, Prince did not leave behind a will, sparking a protracted legal battle over his estate, with dozens of people filing claims of heirship.

The exact value of Prince's estate is unclear but believed to be in the hundreds of millions of dollars. 

The musician's assets will not be distributed to his heirs without a formal court order. If an appellate court rules that rejected claimants could have a claim, Mr Eide said he would consider them, court documents said.

Last month, a US judge blocked a planned release of new Prince music.

The six-song EP "Deliverance" had been scheduled to be released on the first anniversary of Prince's death.