Two men were critically injured Tuesday in the collapse of a third-floor fire escape landing in West Philadelphia, police said.

It wasn’t immediately known why the men were on the landing or why the fire escape collapsed.

The collapse occurred shortly after 10 a.m. in the rear of a building on the 4200 block of Chester Avenue, police said.

A 36-year-old man who suffered head trauma and a 31-year-old man who suffered trauma to the left side of his body were taken to Penn Presbyterian Medical Center. Police said the older man was in extremely critical condition and the other was in critical condition.

An investigation is underway.