ISLAMABAD, Pakistan — Clad in black suits, white shirts and black ties, hundreds of lawyers forced their way into the Lahore cardiology hospital, smashing windows and damaging equipment. Doctors ran for cover, and unattended, panicked patients ran for their lives. The hospital wards were littered with shards of glass and broken furniture.

Riot police used tear gas canisters, water cannons and batons to disperse the intruders. The melee at the hospital, the Punjab Institute of Cardiology, lasted for hours on Wednesday, shocking the country.

In the end, officials said, three patients died amid the chaos. And now at least 80 lawyers have been arrested by Pakistani authorities, while Prime Minister Imran Khan has ordered an investigation.

The lawyers said they were avenging an attack in November by doctors and staff of the hospital, after the lawyers demanded preferential treatment.