Fire crews, police and ambulances dashed to the scene after a carbon dioxide cylinder exploded in the basement of the Catherine Wheel pub in St Augustines Street, Norwich.
After a loud bang startled drinkers, the landlady evacuated the pub and called the emergency services at 8.37pm.
A rapid response vehicle and ambulance officer arrived in three minutes and treated a man after he inhaled carbon dioxide - he was discharged at the scene.
Three fire crews, one from Sprowston, Earlham and Carrow Road, were called after receiving reports of the unsafe cylinder.
A spokesman from the Norfolk Fire and Rescue Service said: 'A carbon dioxide cylinder went off in the basement.'
Firefighters used breathing apparatus and a gas monitor to make the scene safe.
More to come.
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