A seven-tonne aircraft engine has blocked traffic in Sydney's south-west after falling off the back of a truck.

Emergency services were called to Forest Road at Arncliffe about 9:30am on Tuesday, after reports a truck had lost its load.

Police said an aircraft engine weighing about seven tonnes had fallen onto the road from the side of a heavy vehicle tailer.

Officers said the driver had used restraints that were designed to bear a load of 900 kilograms.

Forest Road was blocked for two hours while the machine was salvaged.

Traffic and Highway Patrol Commander, Assistant Commissioner John Hartley, said a passing crane moved the engine and helped minimise traffic disruptions in the area.

"Operators travelling with oversize loads need to take appropriate precautions to ensure their own safety, and the safety of other motorists," Assistant Commissioner Hartley said.

"Incident such as these can lead to serious crashes and it's lucky other motorists weren't injured or even killed."

The 51-year-old truck driver was breath tested at the scene and returned a negative result.

He has been charged with offences relating to driving with an oversize load.

He is due to appear at Sutherland Local Court on November 1.