BBC reports that the nephew Emanuel Bergoglio was seriously injured in the accident which occurred in the Cordoba area, north-east of the capital, Buenos Aires.
The spokesman for the Pope, Francesco Lombardi said that the pope is “profoundly saddened, and that all who share in his grief should unite with him in prayer”.
His nephew and family were reportedly retuning home from a break when their car collided with a lorry shortly before midnight.
Emanuel’s wife, Valeria Carmona was 39, while the two children were Jose, 2, and 8-month-old Antonio. They were all killed.