The US federal government has added about 50 types of cancer to the list of illnesses to be covered by a 9/11 health treatment programme.

The decision entitles 70,000 surviving emergency service workers and other survivors to free care.

The National Institute for Occupational Safety announced the change on the eve of the attacks' 11th anniversary.

Some 1,000 deaths have been linked to illnesses caused by toxic dust issuing from wreckage at Ground Zero.

Construction workers, emergency workers, office cleaners and others all fell ill in the decade after the attacks.

The institute said last June that it was in favour of expanding the existing $4.3bn 9/11 health programme to include people with 50 types of cancer, following a recommendation from an advisory committee.

Cancers to be covered include lung, colorectal, breast, bladder, leukaemia, melanoma and all childhood cancers.

The medical coverage comes under the Zadroga 9/11 Health and Compensation Act, which was signed into law by President Barack Obama last year.

Until now, most of the health compensation was for respiratory diseases linked to the toxic dust and fumes from the fallen towers.

John Howard, administrator of the World Trade Center Health Program established by the Zadroga law, said Monday's announcement marked "an important step in the effort to provide needed treatment and care to 9/11 responders and survivors".

New York City Mayor Michael Bloomberg said in a statement the decision would "continue to ensure that those who have become ill due to the heinous attacks on 9/11 get the medical care they need and deserve".

The compensation has been held up by a dispute over whether there was evidence of a direct link between the World Trade Center tragedy and cancer.