Synthetic cannabis has claimed at least 20 lives in New Zealand. (File photo)

Smoking synthetic cannabis has landed two people in hospital in a serious condition.

A 39-year-old male and 16-year-old female, were admitted to Taranaki Base Hospital's ICU on Sunday.

The man has since been discharged while the teenager remains in hospital on a ward.

Katarzyna Bia??asiewicz Two people were admitted to Taranaki Base Hospital in the weekend after smoking synthetic drugs. (File photo)

In September two men from Waitara came close to dying after using the drugs which police believed was an unusually strong batch.

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In 2017 it's believed 20 people died nationally after smoking the drugs and police are warning against using it in a hope to prevent further deaths.

Detective Sergeant Pat Yates said police officers came across the man, who has admitted to using the drugs, in New Plymouth's CBD late Saturday night or in the early hours of Sunday morning.

"He was clearly under the influence of something and obviously subsequently admitted by ambulance to ICU," Yates said.

"We don't know what else he has taken, if anything."

Yates didn't know how the teenager, who wouldn't speak with detectives, got to hospital or what state she was in when she arrived.

"It's my understanding that when they were admitted they were both in a reasonably bad way."

He said while there had been no deaths associated with the use of synthetic cannabis in Taranaki so far, police wanted to prevent it happening in the future.

"We'd be discouraging people from using it. They don't know what is in it and it has caused significant harm to a lot of people nationally and certainly a lot of people here in Taranaki too.

"The message that we want to get out there is clearly it's not safe to use so don't use it."

In the most serious case in Taranaki during September, CPR was used to revive a man before he was taken to hospital while another man was found unconscious and unresponsive after smoking the drug.

Police described people who had been using the drugs as being in a "catatonic" state and unable to speak.

Nationally the deaths are being investigated and the Chief Coroner and police joined forces to warn people of the perils of synthetic drugs.

Chief Coroner Judge Deborah Marshall said each death was a "tragedy".

"Using any illicit drug carries risks, and in the case of synthetic drugs, they are known to cause potentially fatal seizures," she said.

"I urge anyone considering using this drug not to do so, and for those who are, to reach out to services that might assist them."

Yates said police were continuing to target the sale and supply of synthetic drugs around the region and encouraged anyone with information to contact their nearest police station or Crimestoppers on 0800 555 111.