More than one in 10 trucks on roads in New South Wales were found to be defective during a major crackdown on safety by police.

Traffic and Highway Patrol officers, working alongside inspectors from the Roads and Maritime Service, inspected 13,806 trucks and trailers in the first week of Operation StateTrans.

Police issued 1,609 defect notices for things such as faulty brakes, fuel and oil leaks, steering and other mechanical issues.

They also issued 888 fines and 317 breaches to drivers for a range of licence, registration, fatigue and load offences.

Chief Inspector Phil Brooks said the worst offenders had now been taken off the road.

"We're doing this to make sure that those trucks, those drivers are able to operate safely on our roads," he said.

"During these sorts of operations it's not uncommon to see these sorts of numbers as we make sure that those who are pulling very important goods throughout the NSW road network are doing so safely."

One in five engines tampered with for speed

Chief Inspector Brooks said police also conducted more than 300 engine checks and found 66 trucks were non-compliant or had been tampered with so that they could travel at speeds of more than 100 kilometres per hour.

He said 12 drivers also tested positive for drugs and had their licences suspended for 24 hours.

"We've also had some drivers test positive to drugs with drugs being recovered in some of the trucks during our operation, he said.

"Those drivers that are found to be positive to drugs, driving trucks with trailers that are unsafe to be on our roads, can be a deadly combination."

Operation StateTrans will run for the month of May and will target heavy vehicles across the NSW road network.