A man found in the street with “life-threatening injuries” was the victim of a knife attack, police believe.
The ambulance service alerted officers after paramedics were called to Church Street in Rhyl at 01:40 BST on Tuesday.
A 43-year-old local man is in a serious condition in hospital as a result of “what is believed to have been a knife attack”, North Wales Police said.
Police have cordoned off the street while investigations continue but have said it would soon reopen.
Officers are supporting the man’s family, police said.
Ch Insp Andrew Williams, from North Wales Police, asked anyone who was in the area between 01:15 and 01:30 to contact them.
“I would like to reassure local people that there is no current evidence or intelligence to suggest any risk to the general public,” he said.
“Nevertheless, we will be stepping up patrols in the local area to assist in this reassurance.”