FIVE decomposing human heads were found outside a primary school in the Mexican city of Acapulco, police said, in the latest example of grisly violence gripping the country.

Someone placed a wooden box near the Benito Juarez school in the southern port city today, and "on top of it was a white bag which contained five severed human heads inside," a police officer said on condition of anonymity.

The discovery occurred in full view of young students and pedestrians, sparking fear in the area. Soldiers and police removed the remains and cordoned off the location.

Yesterday in the same city - a major port and tourist resort on Mexico's Pacific coast - police found five decapitated bodies: three badly burned inside a pickup truck, and two others outside the vehicle.

Police said they expected the heads to match the corpses found yesterday.

Acapulco, some 300km from Mexico City, was once a popular getaway for Hollywood stars, but in recent years has turned into a battleground in Mexico's increasingly violent drug war.

Last week thousands of teachers and activists demonstrated in Acapulco after nearly a month of strikes over lax public safety in schools and pleas to authorities to improve security amid threats extortion threats.

Five weeks ago, three heads were found in a plastic bag on a busy street leading into Acapulco. Also in August, suspected traffickers killed and mutilated a man, then left his body parts around the city in a macabre taunt to authorities here.

At least 41,000 people have been killed since 2006, when Mexico launched a military crackdown on powerful cartels, which are themselves embroiled in turf wars marked by kidnappings, mass graves and brutal massacres.