Emergency rooms across the United States saw a big jump in overdoses from opioids last year — the latest evidence the country's drug crisis is worsening.

A government report released Tuesday shows overdoses from opioids increased 30 per cent late last summer, compared to the same three-month period in 2016. The biggest jumps were in the Midwest and in cities, but increases occurred nationwide.

"This is a very difficult and fast-moving epidemic and there are no easy solutions," said Dr. Anne Schuchat, acting director of the Centers for Disease Control and Prevention (CDC).

Overdose increases in some states and cities may be due to changes in the volume and type of illicit opioid drugs being sold on the streets, health officials said.

The report did not break down overdoses by type of opioid, be it prescription pain pills, heroin, fentanyl or others.

The CDC recently started using a new system to track emergency-room overdoses and found the rate of opioid overdoses rose from 14 to 18 per 100,000 ER visits over a year. Almost all those overdoses were not fatal.

The CDC numbers are likely an undercount. Its tracking system covers about 60 per cent of the ER visits in the whole country and some people who overdose don't go to the hospital, Schuchat said.

Opioids were involved in two-thirds of all overdose deaths in 2016. That year, the powerful painkiller fentanyl and its close opioid cousins played a bigger role in the deaths than any other legal or illegal drug.

More recent CDC data shows overdose deaths rose 14 per cent from July 2016 to July 2017, but that data doesn't distinguish opioids from other drugs.