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Emergency services rushed to the nightclub in Adeje in southwestern Tenerife at about 2:30am after receiving reports that roughly four square metres (43 square feet) of its floor had collapsed, the regional government of Spain's Canary Islands said in a statement.
"After the floor collapsed, the people who were inside fell to the basement from the height of approximately one floor," it said.
Firefighters evacuated the nightclub, and the 22 injured were taken to hospital, including two of them in serious condition.
The injuries included broken legs, ankle sprains and bruises. Two French nationals, a Belgian and a Romanian were among those hurt.
Police have launched an investigation into the incident.