Four people have died from drug overdoses in Brisbane over the past week and six more have been left critically ill.

And in Perth three young people died after 91 suspected drug overdoses across four days, described as the biggest spike in recent memory.

It has prompted an urgent health warning from police and paramedics about the risk of taking illicit substances.

In Brisbane, two men, both 39, and two women, 26 and 30, are dead, and six more people have presented to hospitals after overdosing on a combination of alcohol and illicit drugs.

Paramedics were finding people collapsed after drinking and taking either heroin, amphetamine or fantasy, Queensland Ambulance Service’s clinical director, Tony Hucker, said.

“When you combine the two that’s a higher risk combination,” he said.

He said that did not mean taking drugs on their own was safe, but that people could make safer choices that minimise the risk.

“Obviously to manage the risk is don’t take drugs, but we understand the reality out in the community,” Hucker said.

“If you’re going to take one of these drugs, take half a dose when you start, make sure you don’t re-dose in the first 90 minutes, and always make sure you have friends with you that are prepared to look after you.”

Police say there are no known links between the cases.

“While official toxicology results are not yet known, there is information that a range of illicit drugs have been involved,” Det Insp Rod Watts said on Friday.

In Perth, a 21-year-old man, who had been at the Metro City nightclub, and two women aged 23 and 25 all died on 7 December. Police are yet to determine which substances the trio might have taken.

Western Australia’s police commissioner, Chris Dawson, said the three were among 91 reported overdose victims between 4 and 7 December. He had not seen such a heavy toll since Perth was in the grips of a heroin epidemic in the 1990s.

The two women, from Fremantle and Leederville respectively, both showed indications of intravenous drug use and may have taken heroin. They are believed to have separately been at private homes.

“The point I’d stress is there’s a bad batch of drugs out there,” Dawson said on Monday.

“I cannot tell you definitively what type of drug or indeed whether there is a bunch of different substances that are being taken.

“But to lose three young adult lives in the Perth metropolitan area in one day ... Police are duty-bound to warn the community whenever we see a very spiked increase in apparent drug overdoses.”

Emergency services responded to 24 drug overdoses on 4 December, 29 on 5 December, 26 on 6 December and 12 on 7 December, including the three deaths.

Police had singled out the party drug GHB, also known as fantasy, as a possible link to several recent overdoses.

Dawson said police were yet to receive toxicology reports from any of the deaths and that process could take several weeks.

“My message is simple: do not take drugs that are illicit,” he said. “People are dying. We obviously need to bring this to the community’s attention in order that we don’t have more tragedies like we saw on Saturday.

“We certainly had a bad run in terms of overdose deaths 20 to 30 years ago with a bad run of heroin. But certainly, in my recent history, I can’t recall three drug overdoses in one day.”