Guatemala City ? The first tropical storm of the 2010 season hit the Pacific coastline of Guatemala and Mexico on Saturday, killing 12 people under landslides and rockfall triggered by torrential rains.

Agatha’s rains caused a landslide in a precarious hillside settlement of Guatemala City that killed four people and left 11 missing, Guatemalan disaster relief spokesman David de Leon said. Most of the city was without electricity at nightfall, complicating search efforts.

Four children were killed by another mudslide in the town of Santa Catarina Pinula about six miles outside the Guatemalan capital. And in the department of Quetzaltenango, 125 miles west of Guatemala City, a boulder loosened by rains crushed a house, killing two children and two adults, de Leon said.

Agatha formed as a tropical storm early Saturday in the East Pacific and moved over land in the evening along the Guatemala-Mexico border, said the U.S. National Hurricane Center in Miami.