Children as young as 12 are smoking tobacco in illegal shisha dens across Blackburn, officials have claimed.
Blackburn Trading Standards believe up to 12 of the premises are operating in homes and takeaways - in breach of anti-smoking legislation.
Shisha pipes, or hookahs, are filled with flavoured tobaccos but in public places must be used outdoors.
Trading standards officers said anyone caught flouting the law would be prosecuted.
But as well as selling tobacco to people under the age of 18, Blackburn with Darwen Council believe the dens also pose a health and safety risk.
"We suspect that in the borough there are approximately 10 or 12 of these premises which are operating," said spokesman Chris Allen.
"They are dangerous. Children are being allowed into these premises and then the doors are locked behind them - so escape routes will be non-existent should a fire break out.
"To be selling tobacco products to children as young as 12 is absolutely out of order.
"All the resources we have will be targeted towards preventing this from occurring in the future."
One woman from Blackburn, who did not want to be identified, told the BBC her 13-year-old brother regularly attended one such premises.
She said: "He goes every weekend. I think they just sit down and just smoke and chill out and relax. But it's not very good for them is it?"
Earlier in February, a 19-year-old cafe owner was fined £2,000 after causing an explosion while lighting his pipe with a blow-torch.
Mohammed Wasim Natha, of BBQ Base in Darwen Street, Blackburn admitted breaching health and safety laws.