Five fire engines and crews were called to the hospital on Wilmslow Road at around 10.30am this morning.
Witnesses reported black billowing smoke coming from the roof of the three storey Paterson Laboratories.
A spokesman for Greater Manchester Fire services said: "Crews are working hard to tackle a fire involving the first floor plant room and roof space of the Cancer Research UK Institute Manchester building on the hospital site.
"Five fire engines and an aerial ladder are at the scene.
"Firefighters are wearing breathing apparatus and using jets and hose reels to extinguish a fire involving the three-storey office block and labs.
"The affected building has been safely evacuated and other office buildings nearby have also been evacuated. Currently, no buildings containing patients are being evacuated."
A spokeswoman for The Christie confirmed no staff or patients have been affected by the fire.
She said: "All the associated areas have been evacuated, including any patient areas.
"The fire service is on site.
"For staff and patients, if they have not already been evacuated they need to carry on as normal.
"Any patients who are attending for treatment need to attend as normal and access the hospital via the Palatine Road entrance."