Gwilym Evans, 61, was last seen with 13-month-old Liam at his home on Thursday.

More than 60 officers, an RAF helicopter and specialist rescue teams are now combing the north Wales coastline.

Gareth Evans pleads for his son's return

Liam's father, Gareth, begged his father to return his son at a news conference. His wife Ruth sobbed at his side during the emotional TV appeal.

Gareth Evans described his son as ''a happy, lively, noisy little boy whom we worship.''

It now appears Mr Evans and his grandson left home at about 3pm on Thursday.

He was seen shortly afterwards at a petrol station in Princes Drive, Colwyn Bay, where he bought a full tank before driving off towards Conwy.

Police are asking hotels and caravan sites to check for Mr Evans's maroon Vauxhall Vectra car, registration number P59 HEY.

Detective Superintendent Eric Jones of North Wales Police said there was no reason to suspect the child had come to any harm and he appealed to his former colleague to contact him so they could talk things through.

Anyone with information is urged to call a police hotline on 01492 518383.

The two left Gwilym Evans' house in Old Colwyn

Police have been unable to confirm the early theory that Mr Evans could have fallen ill or had an accident close to his home in Old Colwyn and not been able to make his way back.

Trip out in the car

Det Supt Jones said Mr Evans and his wife, Barbara, were looking after Liam while Gareth and Ruth took their three-year-old daughter Sophia to a doctor's appointment.

Liam grew a bit boisterous while Mrs Evans was playing with him, so Mr Evans offered to take the child off her hands.

"At that time she assumed that the child had been taken upstairs or outside as he was due to be fed at 4pm," Det Supt Jones said.

It was only "some minutes later" that she realised he had taken the car, and she assumed her husband had taken Liam out in the local area.

Detective Superintendent Eric Jones: He is a doting grandfather

"After 4pm concern grew for her husband and the child and at 6pm they were reported missing to the police.''

The detective said extensive overnight searches had been carried out in Colwyn Bay, Abergele, Llandudno and beyond, with no results.

"As far as we are aware Mr Evans was in good health apart from an arthritis problem in his back, for which he took some medication, but no tablets have gone missing."

"We are not aware of any history of depression."

'A mild-mannered man'

The most likely explanation for their disappearance was that Mr Evans had had an accident of some sort, he added.

"There is nothing whatsoever to suggest that any harm would befall Liam from the hands of his grandfather. He is a doting grandfather, a mild-mannered man."

Det Supt Jones said Liam's parents were very distressed and police had interviewed them "to get every speck of information from them that might help us find Mr Evans and Liam, for example favourite places that they might have frequented in the past."