Detectives ramped up the search for a missing pensioner after it reached its fourth day since his last sighting.
Granville Muir, 75, from Halifax, was last seen on Saturday morning at his King Cross home and concerns for his welfare are so great police are urging anyone who sees him to call 999.
Mr Muir is diabetic and has short term memory loss, with police describing him as an “elderly and vulnerable man”.
The force held a press conference on Wednesday morning as detectives continued their searches.
Granville is thought to be in either Calderdale or Kirklees.
He is described as six foot tall, possibly wearing a cardigan or blue clothing, walking with a limp and may appear confused.
Chief Insp Justine Plumb said: “We are gravely concerned for Granville’s wellbeing.
“We are carrying out an extensive search in the local area including officers on the ground, our mounted and dog officers and our drone. Our partners from the Fire and Rescue Service and Calder Valley Search and Rescue are also giving invaluable help.”
Police are also urging residents to check outbuildings where Mr Muir may be taking shelter.
Supt Owen West of Calderdale Police, said: “His family are very worried about him and we are too. We are concerned he may have come to some harm.
“Such is our concern for Granville that we are asking anyone who sees him to call the 999 emergency number rather than the 101 non emergency number.”