STATEN ISLAND — There were four fatal Staten Island overdoses in four days last week as the borough continues to battle an opioid epidemic, District Attorney Michael McMahon announced.

Nine people overdosed around Staten Island from Thursday to Sunday, including the four deaths, McMahon announced on Twitter.

Over the last 4 days, 9 Staten Islanders have experienced a drug overdose. Four of them have lost their lives. — Michael E. McMahon (@StatenIslandDA) October 2, 2017

So far this year, 73 people have died from overdoses on Staten Island and 138 people were saved using naloxone, a drug that effectively reverses the effects of an overdose, according to the DA's office.

The city has been in the throes of an prescription drug and heroin epidemic for more than a decade with Staten Island and The Bronx being hit the hardest.

The past two years have gotten more deadly due to the introduction of the synthetic opioid fentanyl to batches of heroin, officials said.

Fentanyl, which is 50 times more powerful than heroin, is being smuggled in from China and Mexico and added to batches by dealers to increase profits and potency, experts said.

► READ MORE: The Rise of Fentanyl, the Drug Driving Up Deadly Overdoses Across the City

Last year, 1,374 people died from overdoses around the city — a 46 percent increase from 2015 — with fentanyl being found in 44 percent of them, according to the Department of Health.

McMahon previously said that more than 50 percent of the drug cases his office sees involves fentanyl, but that number could be as high as 75 percent.

A spokesman for the District Attorney's office said investigators have not determined what caused the latest spike in overdoses and testing hasn't come back to show if fentanyl was found in any cases.