Firefighters diagnosed with certain cancers in NSW will soon be able to claim compensation without having to prove themselves it was because of their work.

The state government on Wednesday introduced draft laws that will make it easier to access entitlements by automatically presuming firefighters acquired one of 12 cancers while on the job.

It will instead be up to insurers to prove the cancer was not a result of firefighter duties under the proposed changes.

"The onus has historically been on firefighters and it is a difficult task when all the science, all the studies and all the understanding is that all firefighters go into unknown hazardous situations," NSW Emergency Services Minister Troy Grant told reporters in Sydney.

Firefighters are often exposed to a mixture of chemicals, carcinogens and other elements that are identified as being contributors to cancer, Mr Grant said.

Fire & Rescue NSW deputy commissioner Mal Connellan said a small number of firefighters are diagnosed with cancer every year and have faced a battle to prove the cancer is linked to their work.

"It is an extremely distressing time and this legislation removes that burden from them and their families," he told reporters.

If passed, the legislation will apply from September 27. Firefighters who have made a previously rejected claim will be allowed to reapply under the new laws.

Both voluntary and paid firefighters will be eligible, as will firefighters who are diagnosed with cancer after they have left the industry.

The cancers include brain, leukaemia, breast, testicular and bladder cancer.