LOWELL -- Police are warning the public about a surge of opioid overdoses in the city.

In the last five days, 10 people have overdosed, including four fatal overdoses, the Lowell Police Department announced in a press release Thursday evening.

"If you are going to use just be extra vigilant in the next couple days," Lowell Fire Chief Jeff Winward warned. "Check on your loved ones."

Winward and police urged against using opiates and to call 911 immediately if you witness a possible overdose.

Police believe fetanyl is being mixed with heroin, cocaine and other drugs causing the spike. There have been several cases of opiate-laced pills being passed off as Xanax or other prescription medications, according to police.

"We see these wild swings," Winward said. "It can be quiet for weeks and then it really spikes up."

On Tuesday, authorities said the death of a person found next to trash containers in the Acre neighborhood was caused by an overdose.

Previously, officials warned of a spike in the region, after three people died from suspected overdoses over the first weekend of December.

An opioid task force convened by Middlesex District Attorney Marian Ryan will meet Friday at Lowell General Hospital for its scheduled meeting to discuss monthly and yearly overdose numbers.