Police and health officials have issued a public warning following a rash of nearly a dozen non-fatal drug overdoses in Vancouver's Downtown Eastside in a single day. 

There were 11 overdoses reported from a variety of service providers on Monday, police said, and though the cause hasn't been determined there is concern that the powerful opioid fentanyl was involved.

"The suspected drug appears to be purple in colour and overdoses may be a result of the consumption of fentanyl," Staff Sgt. Randy Fincham said in a statement.

Police said early signs of a fentanyl overdose include severe sleepiness, a slow heartbeat, trouble breathing, cold, clammy skin and trouble walking or talking.

Anyone who sees someone they believe to have taken illicit drugs exhibiting those symptoms should call 911 immediately, Fincham said.

Police also urged drug users to never inject, snort or swallow drugs alone.