LONDON — Several people suffered "breathing difficulties" at the London Aquatics Centre following the release of gas, the Queen Elizabeth Olympic Park said in a statement on Wednesday.

Firefighters said they were responding to reports of a "chemical incident" at the center while the London Ambulance Service confirmed they were treating a number of patients.

The ambulance service called it a "major incident" at the center, which held aquatics events during the 2012 Olympics.

Images posted to social media showed multiple ambulances and fire engines at the scene.

London Mayor Sadiq Khan said he was in close contact with emergency services and said a number of people were being treated.

"Please avoid the area which has been cordoned off and evacuated," Khan said in a tweet. — Euronews