At least 19 people were killed in southern Mali when a large gold mine collapsed, a local official said Wednesday.

Six people were injured in the collapse on Monday night and Tuesday morning in Sikasso province, said the official, adding that it was a large mine that also had several other smaller operations running inside.

The cause of the collapse was not immediately known.

Despite vast gold deposits in southern Mali, the West African country is considered by the United Nations to be among the world's poorest.