CHICAGO (CBS) — A long stretch of southbound Lake Shore Drive was shut down during the afternoon rush Thursday after a major crash.

Police said around 3:10 p.m., an 80-year-old man was driving south on Lake Shore Drive approaching the Belmont Avenue exit, when he suffered an unknown medical emergency.

READ MORE: Child In Critical Condition After Being Pulled Out Of Pond At Lake In The Hills Golf Course

The man became unresponsive and hit a guard rail, causing his car to spin out and block southbound traffic, police said.

The man was pronounced dead at the scene.

Initially, police shut down southbound Lake Shore Drive from Irving Park Road to Fullerton Drive. By 4:30 p.m., the closure had expanded so that the southbound Drive was closed from its start at Hollywood Avenue to Belmont Avenue, according to the Office of Emergency Management and Communications.

By around 6 p.m., all lanes had been reopened.

MORE NEWS: Dolton Gas Station Attendant Richard Williams Charged With Beating Woman Who Says She Just Wanted To Use Bathroom

The police Major Accidents Investigation Unit was investigating Thursday afternoon.