MADRID — The well is over 300 feet deep, but less than a foot wide. And somewhere in its depths a 2-year-old boy is believed to be trapped.

Frantic efforts to rescue the toddler, Julen Roselló, have been underway in the countryside northeast of the port city of Málaga after he was said to have slipped down the well while his parents were preparing Sunday lunch.

About 100 rescuers have been working at the site, covered round-the-clock by the Spanish news media, while Julen’s father has made repeated pleas on television for every effort to be made to find his son alive.

On Wednesday, the authorities in southern Spain announced that according to a preliminary DNA test, hair found in mud excavated from the well was the boy’s, confirming his presence. He is believed to be more than 250 feet underground, beneath earth dislodged by his fall.