Between 20 and 25 bodies, thought to be the victims of drug gang violence, have been found in an abandoned silver mine in southern Mexico, officials say.
The bodies appeared to have been thrown down a 200m (650ft) ventilation shaft over a period of time, police said.
The mine is near the city of Taxco in Guerrero state, a focal point for drug-related violence that has claimed some 23,000 lives nationwide since 2006.
A tip-off from a person arrested on Friday sparked the search.
Police and soldiers have been using breathing equipment as they descend deep underground to recover the bodies.
Many of the corpses had their hands and feet tied, Mexican media reported.
The mine is located near Taxco, a colonial era city popular with tourists.
While much of the drug violence over the past four years has been in northern Mexico, in particular in areas bordering the US, other regions have not been immune.
Guerrero, in the south and with a Pacific coastline, has also seen vicious bouts of bloodshed amid bitter turf wars for control of the trade in illegal drugs.