The five, one woman and four men, accidentally made contact with high voltage cables while hanging ornaments on an artificial Christmas tree made of iron and wires, local press reported.
The dead were between 17 and 24 years old.
The incident occurred in El Carmen Frontera, on the border with Mexico.
Tweets showed the tree lying on its side in the town’s park.
Rescue workers said the five had died instantly.
Residents said the Christmas tree had been erected in the same place for the past 20 years without any problems.