An investigation into an incident which led a pub to be evacuated when staff and revellers suffered breathing difficulties is continuing.
Police were called to The William Hedley in North Road in Durham at 5.45pm yesterday after reports of a noxious substance being sprayed.
County Durham Fire and Rescue Service was also called to the scene.
The incident happened on the busiest day of the year for the city, with around 200,000 people visiting for the Durham Miners' Gala, which saw Labour leader Jeremy Corbyn and award-winning director Ken Loach among its guest speakers.
A spokesman for Durham Constabulary said: "A small number of staff and customers reported symptoms of irritation to the nose and eyes and difficulty breathing, however, there have been no serious injuries or lasting effects.
"The premises were quickly declared safe, but remained closed as a precaution.
"The substance has not yet been identified and inquiries are ongoing."
Detective Sergeant Richards, of Durham City CID, said: “This was understandably alarming for those present, but despite the premises being busy, there have fortunately been no reports of any lasting effects.
“A police investigation is now underway to determine the nature and source of the substance, and I would invite any person who has information regarding this matter to contact Durham Police on 101, or Crimestoppers on 0800 555 111.”
Firefighters and two appliances remained at the scene until 7.20pm, with ventilation fans used to clear the bar of fumes.