Mahathir, who has set up a new political party to oust Prime Minister Najib Razak in elections due by mid-2018, was answering questions Sunday at the forum, hosted by his party, when chaos erupted.
Shoes, water bottles and chairs were flung at the stage before two flares were ignited, filling the hall with smoke and turning it bright pink.
Mahathir was safely escorted out of the hall. Forum organizer Syed Saddiq Syed Abdul Rahman said several people were injured but couldn't give details on the exact number or their condition. He said police detained two people.