Police in the western city of Benguela issued a statement "announcing the death of eight citizens for reasons that remain to be determined", adding that an investigation had been launched.
Nelson Sul, an Angolan journalist at the Afromusic festival on Sunday evening, said the toll could be higher.
"There are more bodies in morgues in the city. The criminal investigation service told me that the death toll was 20," he told AFP.
The event brought together leading Angolan musicians including stars of kizomba, a popular local genre.
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