The death toll from a rash of overdoses within the last 24 hours has risen to four, Vancouver police said Wednesday just hours after issuing a public warning.

Police had initially reported three deaths but Wednesday afternoon were called to the scene of another overdose — this time, a man in his 50s.

Police say there have also been 17 non-fatal overdoses in the city — most of them on the Downtown Eastside.

Their warning comes in the wake of recent concerns over stolen fentanyl patches and counterfeit percocets.

"Various drugs from the scenes of the overdose deaths have been seized and forwarded to Health Canada for analysis, but investigators expect to find fentanyl in many of those samples," said a statement from Const. Brian Montague.

Fentanyl is a synthetic narcotic that is 50 to 100 times more toxic than other opioids, the statement said.

Among the three dead, a 24-year-old man in Downtown Vancouver, a 35-year-old man in East Vancouver and a woman believed to be in her mid-20s on the city's Downtown Eastside.

Police say the public warning applies to both "seasoned" and recreational drug users.