Up to 40 people are feared dead after a massive fire broke out during a rave at a converted warehouse in Oakland, California.

The blaze began amid an electronic music performance at the warehouse, which had been converted into an artist’s collective.

Nine people were initially confirmed dead but a full search had been delayed after the building’s roof collapsed, and dozens remained missing. Officials said 50 or more people had been inside.

The county coroner's office said it was preparing for up to 40 bodies, and a police spokesman said the victim count could well rise that high.