MEDELLIN, Colombia — A huge explosion ripped through a cocaine laboratory in Colombia's drug capital of Medellin today, killing eight people, wounding 25 and destroying a dozen houses, police sources said.

A chemical reaction apparently caused the explosion in the secret laboratory in a house in central Medellin. It touched off dynamite stored in the basement of the house, causing a huge explosion, the sources said.

Residents said the explosion, which damaged nearby buildings, was heard throughout Medellin, headquarters of Colombia's biggest cocaine cartel.

A senior police officer said eight people were killed, including three children, and 25 were injured, five seriously. Twelve houses were destroyed and another 15 badly damaged, he said. Some of the casualties were pupils at a local school.