LONDON -- A dozen people sought treatment for burns early Monday morning after someone involved in an argument at a London nightclub sprayed others with “acid,” according to police.

London’s Metropolitan Police service said in a statement that two of the victims, both men in their 20s identified only as “victims 1 and 2,” remained hospitalized in stable but serious condition.

The police said the substance sprayed into the club was “yet to be identified, but it is believed to have been acidic.”

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No arrests were made, but police said it did not appear gang-related and they appealed to anyone with information on the incident at the Mangle E8 nightclub in East London’s trendy Dalston neighborhood to come forward.

The police statement said a disagreement between two groups led to ”a noxious substance being sprayed by a male suspect directly at Victims 1 and 2.”

Witnesses told British media outlets that between 400 and 600 revellers still at the club at 1 a.m. were evacuated. It was busy as Monday is a national holiday in the U.K. for Easter.

Nima Navazande, who works at the nearby Martello Hall bar, told CBS News partner network Sky News that her manager was on his shift when the incident played out, and he “heard somebody saying that someone was attacked with liquid acid.”