Another four people were injured when a violent storm suddenly hit Praia Grande, near the port city of Santos, where the lightning strike happened yesterday.
Police in Santos didn't know the condition of those injured. Local media reported city firefighters saying that among the dead was a pregnant woman, her husband, her aunt and uncle.
Violent storms have ravaged southeast Brazil in recent days, with the metropolitan area of Sao Paulo being especially hit hard.
In the early hours of yesterday, a storm downed scores of trees across the area of 20 million, wreaking havoc on transit after more than 100 stoplights malfunctioned.