Julen Rosello's father at the site as efforts to recue him continue. (AFP)

Highlights Julen Rosello fell down very narrow shaft more than 100 metres on Sunday

The chances of finding the boy alive now appear slim, say official

Plan is to dig deep tunnel, manually carve a passage to the well, he said

Rescuers searching for a toddler trapped for a week in a well in southern Spain began drilling a tunnel on Saturday, in the latest bid to reach the boy as part of a massive operation to find him.

Julen Rosello fell down a very narrow shaft more than 100 metres (330 feet) deep on Sunday while playing as his parents had lunch nearby in the town of Totalan near Malaga.

A giant drilling machine was installed Saturday at the site in a bid to make a parallel tunnel and excavation started in the afternoon.

"We hope to achieve this as soon as possible as conditions and that conditions from now will be a bit more favourable," said engineer Angel Garcia Vidal, who is overseeing the operations.

The job will take about 15 hours if conditions are favourable, he said. But the chances of finding the boy alive now appear slim.

The plan is to dig a sufficiently deep tunnel after which miners will manually carve a passage to the well.

"It is surprising to see so many machines, sophistication, so much energy, manpower and work deployed to make this rescue possible," said Juanma Moreno, president of the regional government of Andalusia.

He praised a "huge wave of solidarity, involving not just local residents but people from all over Andalusia and Spain who wanted to participate".

Spanish media, which have been covering the rescue operations round-the-clock, have reported that Julen's parents lost another child, aged, three in 2017. The child had cardiac problems.

The paramilitary Civil Guard have questioned both parents and an entrepreneur who dug the well, a police spokesman said, adding that this was routine in such investigations.

The well was unmarked at the time of the accident and regional authorities in Andalusia said the necessary permission had not been sought before it was dug.