At least 13 people have died in a fire that engulfed three nightclubs in the south-eastern Spanish city of Murcia.

The blaze broke out in the Fonda Milagros nightclub - known as La Fonda - early on Sunday morning.

It then spread to neighbouring clubs as patrons rushed to escape the packed dancefloors, police said.

Family members celebrating a birthday were among the dead, according to local media. Rescuers are still searching for those who are unaccounted for.

One of the birthday party attendees - who was at the club with his cousins and aunt - said he returned home during the chaos, only to be told that one of his cousins had not left, La Verdad de Murcia newspaper reported.

It is not clear if the cousin was among those confirmed dead.

"I think we left 30 seconds to one minute before the alarms went off and all the lights went out (and) the screams saying there was a fire," one survivor told the Reuters news agency.

The club is located in the Atalayas area in Murcia, and the fire is believed to have started at around 06:00 (04:00 GMT).

It is still not clear what caused the blaze. But Murcia's Mayor Jose Ballesta told reporters earlier in the day that the fire had broken out on the first floor of the club.

"Anyone responsible, whether they are part of the government or an individual, will be brought to justice," he said.

Diego Seral, of the national police, said the roof of La Fonda had collapsed, which was making it challenging to locate victims and work out what had happened.

A 28-year-old woman sent a voice note to her mother when the fire had started, according to the La Verdad de Murcia newspaper, saying: "Mummy, I love you, we're going to die."

She had gone out with her partner and some friends from the nearby town of Caravaca de la Cruz. It is not clear if she survived.

"They went because in Caravaca there are no nightclubs," the woman's father, named as Jairo, told the paper. "It was the second time she had been."

Four people are being treated in hospital for smoke inhalation, and a local sports venue is being used to provide counselling for those affected.

"We are devastated," Murcia Mayor Jose Ballesta said. He has decreed three days of mourning in Murcia.

Spain's King Felipe VI has been among those to express his condolences.

"Pain and dismay as the tragic day in Murcia has progressed," wrote a representative for the King on X (formerly Twitter).

"Our solidarity with the families of the victims and with the entire city."

The fire is believed to be the country's worst such blaze in more than 30 years. In 1990, 43 people were killed in a nightclub in Zaragoza.