A young boy was fighting for his life Thursday after falling down an elevator shaft in a Bronx building, authorities said.

Firefighters found the unconscious child, who police sources said is 6 years old, on top of an elevator on the basement level of 1235 Grand Concourse just after 12:45 p.m., according to the FDNY.

The boy was taken to Harlem Hospital in critical condition with injuries to his legs and head, according to FDNY and police sources.

It was unclear how the child fell or what floor he fell from.