At least 21 people have been injured after a balcony of a popular restaurant in South Africa's Cape Town caved in on Thursday evening.

Reports say that the restaurant's patrons were celebrating First Thursday, a cultural event held in Cape Town and Johannesburg every first Thursday of the month.

“The exact circumstances are not known. A total of 21 patients were taken to various hospitals,” Cape Town’s disaster risk management spokesperson, Charlotte Powell, told the Daily Maverick news website.

The building that housed the restaurant was old, its maintenance manager Rashied Kamaldien told South African broadcaster eNCA.

He also said that the building had initially been designed for residential flats.