Most of the injured suffered broken bones and bruises, with two people in critical condition. Two French nationals, two British men, a Belgian and a Romanian were among those hurt.
Forty people were injured after part of the floor at a packed nightclub on Spain's holiday island of Tenerife collapsed on Sunday, sending revellers plunging into the basement, officials said.
Rescuers rushed to the Butterfly Disco Club in Adeje at about 2:30 am local time after a roughly four square metres (43 square feet) of its floor gave way.
The injured included two French men, two British men, a Romanian man and a Belgian woman, local firefighters said.
"After the floor collapsed, the people who were inside fell to the basement from the height of approximately one floor," the regional government of Spain's Canary Islands said.
Video posted by the local fire department on Twitter showed firefighters picking through rubble with their hands in the basement of the nightclub located in a shopping mall.
Authorities said the basement was not in use and so was empty at the time of the collapse.
Britain's foreign office said it was in contact with "a number of British nationals" who had been injured in the incident.
Videos posted on social media showed emergency services workers attending to people on the ground or on benches outside of the nightclub.
Emergency services took 21 people to hospital and treated another person at the scene who was released, the regional government said.
Another 18 people went to hospital by their own means to be treated, the mayor of Tenerife said.
The injuries included broken legs, ankle sprains and bruises. Two of the injuries were deemed serious.
The Butterfly, a popular gay nightclub in Tenerife, features drag shows and Go-Go dancers on Saturday nights, according to its Facebook page.
Video posted by Tenerife firefighters showed a gaping hole right in front of the club's stage.
The club had its licence in order and did not appear to be overcrowded when the floor caved in, the mayor of Tenerife said.
Police have launched an investigation into the incident.
Located off the west coast of Africa, the Canary Islands welcomed 13.3 million foreign tourists last year, making it Spain's second most visited region after Catalonia.