Four people died after being trapped in a tunnel deep under an old Mexican estate where they were said to be searching for buried treasure, emergency workers said on Tuesday.

Two rescue workers died in a laborious rescue attempt in the town of San Jose Rincon in Mexico state on Monday, scaling down a makeshift tunnel 45 feet (15 meters) underground, that stretched some 150 feet (50 meters) long, local press reports said.

"There are rumors that they were looking for treasure. They were suffocated by toxic gases," said a local representative of the civil protection force.

In some small towns in Mexico legends persist that wealthy landowners hid loot under sprawling haciendas now abandoned.