At least four people were killed and 21 others injured when the roof of a restaurant in Spain's popular tourist island of Mallorca collapsed Thursday, local rescuers said.

"There are four dead and around 21 injured," an emergency services spokeswoman said, adding that "several nationalities" were among the victims.

The emergency services wrote on social media platform X that seven of the victims were in a "very serious" state and nine others had "serious" injuries, with different hospitals admitting them.

The two-storey building collapsed late Thursday afternoon in the Playa de Palma area to the south of the Mediterranean island's capital Palma de Mallorca.

Firefighters were deployed in numbers, while ambulances whisked the victims to the hospital and the street was sealed off by police to allow rescue teams to go about their work, an AFP journalist saw.

Rescuers were continuing to work at the scene to find further people stuck under the rubble, they wrote on X.

The exact cause of the collapse remained unknown.

One firefighter described a "nightmarish" scene to the newspaper Ultima Hora, saying that when he arrived, people were crying and screaming around the rubble piled up on the ground floor.

Spanish Prime Minister Pedro Sanchez conveyed his condolences to the victims' families on X, saying he was "closely following the consequences of the terrible collapse."

The central government was prepared to send "all the necessary resources" to help the regional authorities cope, he added.

Sanchez said he had spoken to the president of the Balearic Islands region, where Mallorca is located, and to the city's mayor.

Balearic Islands President Marga Prohens said on X that she was "shocked" by the news, adding she was sending "love and warmth to the families of the four people who have lost their lives."

Mallorca is known for its pristine waters and beaches, and the Balearic Islands attract more tourists than all Spanish regions after Catalonia.

More than 14 million tourists visited the islands last year, according to official figures.

Thursday's collapse took place at the start of the archipelago's high tourist season, on a beachfront avenue home to several shops and entertainment venues.

The 2009 collapse of a three-story building in Palma de Mallorca killed seven people, including two Germans and three Colombians.