One person is in a life-threatening condition after taking what were thought to be contaminated drugs, police have said.
Overnight a number of people in South Tyneside were taken to hospital after falling ill.
Northumbria Police said it believed they had all taken illegal drugs, although the exact type is not known.
The force has urged other drug users that a possibly tainted batch is in circulation.
Several people have been arrested and are being questioned by police.
Two people were initially in a life-threatening condition but one improved later.
Ch Supt Graham Davis, of Northumbria Police, said: "Whilst we don't know the exact drug, I'd urge anyone who may be thinking of taking illegal drugs to be aware of the heightened risk and be very cautious.
"Anyone who has taken drugs and feels unwell should seek medical attention immediately."