Essex drug deaths: Substance tests 'may take some time'
Substances thought to be linked to six deaths may not be identified for "some time", police said.
Three women and three men died within a six-mile (10km) radius in south Essex between Sunday and Tuesday.
Essex Police is investigating the sale of Class A drugs and urged people not to buy, sell or take them this weekend.
Ch Supt Kevin Baldwin said: "Our focus continues to be on what, if any, link there is between these deaths and what substances these people have taken."
He added: "Specialist tests are being carried out to establish what substances are involved. But these tests are complex and may take some time to complete."
He also warned against speculation about the kind of drug involved in the cases, saying it could lead to people being misinformed, which "could cost further lives".
Public Health England advised drug users to be "extra careful about what they are taking" and not to use when they are alone.
One of the six victims was named as Cian Daly, 20, from Leigh-on-Sea, who was found dead on Monday.
A woman in her 30s was found dead in Southend on Sunday, and the body of another woman in her 30s was discovered on Monday in Westcliff-on-Sea.
On Tuesday, a man and woman in their 40s on Canvey Island, and a man in his 20s in Benfleet, were found dead.