Sub-aqua experts were joined by other divers and members of the Holyhead Coastguard when the alarm was raised at the Dorothea Quarry in the Nantlle Valley, Gwynedd, on Sunday.

The quarry is popular with diving enthusiasts

The 300 foot-deep quarry is considered one of the best freshwater diving sites in the UK, but has claimed at least 20 lives in the past decade.

The search for the missing man - aged 57 and from Oldham in Greater Manchester - began at 1130 GMT on Sunday, but was abandoned as light began to fade.

It was resumed early on Monday morning.

It is understood the police's joint force diver support unit hope to use a remote-controlled device, known as an ROV, fitted with a camera to carry out the search.

The extreme depths of the quarry make it unsafe for divers to explore in person.

It is thought the missing man had set out to reach a depth of 100m using a "mixed gas" diving unit, which lets divers reach greater depths than conventional diving equipment.

Earlier this year, the quarry's owner urged enthusiasts to stay away after the death of Paul Amison, 32, from Staffordshire.

Glyn Small said he had made repeated efforts to prevent thrill-seekers using the area, but all his attempts to block access had been ignored.

Blocked off

Just days after the death in February, he had to ask a group of divers from Cambridgeshire who were at the quarry to leave.

He said the roads into the quarry had been closed off with 30 tonne boulders and huge trenches, but groups had still managed to get into the site.

"I hope the people who are doing this have a conscience because these deaths need not have happened," he said.

Mr Small has talked of plans to create a proper scuba-diving centre at the quarry, but any such development would be manned by qualified staff and will have safety resources including a rescue boat, a helipad and a portable hyperbaric chamber.