LOWELL — A spike in overdoses over the last three days has city officials worried that a particularly deadly batch of heroin or fentanyl is being sold in the region.

There have been 20 overdoses in Greater Lowell since Friday, fire Chief Jeff Winward said. None of them were fatal, but only because first responders were able to reach the victims and administer Narcan in time.

“We’re asking people to keep a close eye on things,” Winward said. “Certainly don’t use if you’re by yourself, and watch your loved ones if they have an opioid addiction.”

Trinity EMS, which provides ambulance service for Lowell and several surrounding towns, tracks overdoses and notifies local officials if its EMTs are see an abnormal spike in overdoses.

Last March, city officials and District Attorney Marian Ryan issued their first ever public warning about a deadly batch of heroin, which appeared to have caused six near-fatal overdoses in a 15 hour period.

After the announcement, the worrying increase in overdoses stopped. City officials are hoping their latest warning will have a similarly positive result.

As of 2:30 p.m., there had only been one overdose in Lowell on Sunday.

“If you want to solve problems you’ve got to deal with problems,” Mayor Bill Samaras said. “There’s some serious stuff that’s out there on the street that can be harmful. This stuff — the slightest misuse of it can lead to a death. Just the smallest bit, the size of a salt grain, can have a deadly effect.”

The city urges its residents not to use opioids or other drugs, but encourages anyone who is using to make sure that they are not alone and that they have Narcan available.

Anyone who would like help entering treatment can call firefighter Kevin Jones, who helps lead the Community Opioid Outreach Program, at 978-674-1224.

Anyone who witnesses an overdose is asked to call 911 immediately.

Follow Todd Feathers on Twitter @ToddFeathers.