GENERAL SANTOS, June 9 -- The school year here was only a few hours old when the ground heaved. Children who had just come back from the summer break were sent running into the streets as walls cracked around them, and by Monday afternoon a fast-food restaurant in the city center had folded into a heap of broken concrete, with police picking carefully through the slabs.

The earthquake that struck off the southern island of Mindanao measured magnitude 7.8, according to seismologists, after early readings ran higher and were revised down. Philippine authorities said at least 32 people were killed and more than 200 injured, a count that rose through the day as rescuers reached the buildings that had come down. A tsunami of roughly a meter p...