(AAP) — Fairfax Media journalists who’ve walked off the job for a week say the drastic strike action is warranted because slashing more staff risks transforming Sydney and Melbourne into one-newspaper towns.

Reporters at the Sydney Morning Herald and The Age went on strike on Wednesday afternoon after Fairfax revealed about 25 per cent of the jobs at its major newspapers would be cut.

Some 125 staff are in the firing line.

Herald journalist Sean Nicholls says staff are “shocked and appalled” by the unprecedented cuts which he says posed an “existential threat” to both papers.

Nicholls says the strike could continue until Tuesday when the federal budget is handed down in Canberra.

Readers needed to know Sydney and Melbourne were at risk of becoming one-newspaper towns with a virtual Murdoch monopoly, he told reporters in Sydney.

“That is an appalling situation and threatens the very pillars of democracy,” he said.

Fairfax, in an internal note, said the redundancy program was expected to result in “significantly fewer editorial management, video, presentation and section writer roles”.

Fairfax is slashing costs by $30 million in the face of declining advertising and circulation and told staff it’s looking to cut positions across The Sydney Morning Herald, The Age, Brisbane Times and WA Today.

The company axed 120 editorial jobs from its newsrooms in Sydney and Melbourne a year ago.

Some 474 journalist positions have been lost since 2011, according to the Media, Entertainment and Arts Alliance union, leaving just under 500 positions left.

The Age’s social affairs reporter Miki Perkins says her colleagues are despondent about the 150-year-old institution’s future.

“We just can’t see how we can continue to do what we’ve always done with such big cuts,” she told AAP.

“If you keep cutting journalists you lose quality coverage and that includes things like the federal budget.”

The Herald and The Age will continue to appear in print and online over the coming days.

Usually during strikes stories are written by management and sourced from newsagencies such as Australian Associated Press.

The MEAA says Fairfax is failing its audiences and leaving journalists who remain behind “having to work harder and harder to plug the gaps”.

Staff have one week to reapply for new roles being advertised or take a redundancy.

Fairfax in a statement said it was disappointed staff were taking “unprotected industrial action after a month-long consultation period about necessary changes in our metro media business”.

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