Clubbers at a Tiger Tiger bar in London were treated in hospital after reportedly being given caustic soda instead of salt with their tequila slammers.
Four women and a man were left vomiting after downing shots at the venue in Haymarket last month.
The venue was shut down after emergency services were called to the scene last month.
It is believed staff may have accidentally filled salt pots with caustic soda, often used as a cleaning product, The Sun reported.
A source told the newspaper: “A group of four women and a man necked the tequilas and used salt and lemon to soften the taste, then began to retch. One girl keeled over.
“Despite music blaring, everyone knew something was wrong. There was panic. People thought it was some kind of terrorist incident.”
According to the publication, one of the victims is still requiring hospital treatment more than a month later.
The Metropolitan Police said it was not being treated as suspicious.
A spokesman said in a statement: “Police were called at approximately 10.50pm on Tuesday, 7 December following reports of four people who had suffered burns after coming into contact with a substance, believed to be a strong alkali, at a venue in Haymarket, W1.
“The four people - all female - received treatment at the scene before being taken to hospital; none of their conditions are life-threatening.
“A fifth, person - a male - also came into contact with the substance but has declined hospital treatment.
“The venue was closed as a precaution. The incident is not being treated as suspicious and there have been no arrests. The Health and Safety Executive has been informed.”
Tiger Tiger, Novus Leisure and the Health and Safety Executive have been contacted for comment.
