West Australian police have expressed alarm after three young people died among 91 suspected drug overdoses across a four-day period.

Three young people are dead after 91 suspected drug overdoses in Perth across four days, described as the biggest spike in recent memory.

A 21-year-old man, who had been at the Metro City nightclub, and two women aged 23 and 25 all died on Saturday, with police yet to determine which substances the trio might have taken.

WA Police Commissioner Chris Dawson says they were among 91 reported overdose victims between Wednesday and Saturday, adding that he hadn't 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," Mr Dawson told reporters 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 Wednesday, 29 on Thursday, 26 on Friday and 12 on Saturday including the three deaths.

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

Mr 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 20-30 years ago with a bad run of heroin. But certainly, in my recent history, I can't recall three drug overdoses in one day."