There is no guarantee some of those affected by a bad batch of synthetic cannabis will survive, a doctor says.

In the past 48 hours, 10 people have been taken to Christchurch Hospital after smoking the drug.

They were admitted separately and have come from all over the city.

One of those treating them, Dr Mark Gilbert, said they had suffered symptoms including seizures and heart attacks and three remained in the Intensive Care Unit.

"These 10 will probably be ok but certainly some of them have gambled with their life and there is still some critically unwell people in the Intensive Care Unit so we can't guarantee that they'll live."

All had taken either AB or AMB-FUBINACA which had been linked to numerous deaths in the North Island in the past year.

"Synthetic cannabis is a very dangerous drug, there's no safe level to smoke and we strongly advise, particularly at the moment where there seems to be a bad batch in Christchurch, that people stay away from smoking even small amounts of this."