The roof partially collapsed at the Blinking Owl Cafe in Rayleigh on Thursday while customers were eating.
A lorry with a crane on the back had become tangled in overhead power wires, which caused the chimney to topple.
The man being treated in hospital was injured by falling wreckage but was said not to have been seriously hurt.
The driver of the lorry and another person have been treated for shock.
Gas and electrical engineers, as well as structural engineers from the local authority, were called to the site to make the scene safe.
Station Officer Doug Sylvester, from Essex Fire and Rescue Service said: “The HGV was carrying a container and a small crane which helps it load and unload had been left up.
“As it was driving out of the café’s car park the crane was caught on overhead power cables which in turn pulled a chimney crest down from the roof of the café.
“This chimney crest then went through the roof of a lean-to which is used as part of the seating area for customers.
“It completely destroyed the lean-to which also took part of the main building with it.”
Category: Accident Report