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The agency would be set up within 100 days of a new Government, and has a parliamentary majority.
Solid Energy, which bought the closed Pike River Mine in 2012, two years after the explosion that killed 29 men, is being wound up and will cease to exist by March next year.
In February, the Government ordered the State-owned enterprise to stop the permanent sealing of the portal to allow an unmanned re-entry of the stone drift leading into the mine. Since then, it has been looking at some sort of robotic entry.
Solid Energy chairman Andy Coupe said in February he would resign sooner than let anyone enter the unsafe mine.
However, most of the families have been pushing for a manned re-entry of the drift, and on Tuesday most political parties signed up.
Mr English said in response the agreement would not make things any safer. He hoped the unmanned re-entry would happen before the end of the year and there would be further discussions after that.
He did not support changing the health and safety legislation, which every other New Zealander had to meet.
However, Labour Party leader Jacinda Ardern said re-entering the drift would mean they could recover some of the men, and evidence of the cause of the explosions.
"That will help deliver justice and answers, and bring the men home to their families.
"Labour pledges to the families of Pike River, and to all New Zealanders, that we will undertake a safe re-entry of Pike River Mine,'' Ms Ardern said.
The commitment was signed on Tuesday by the leaders of Labour, United Future, Maori Party, and the Greens. New Zealand First supports re-entry but did not sign.
Meanwhile, the latest robot technology to explore the mine drift is due in the country in November.
Environment Minister Nick Smith said yesterday work on unmanned exploration - agreed to in February - was progressing as quickly as possible.
"A preferred drill site has been selected, the pipe has been ordered and the new robot technology is due in New Zealand in November. The programme of work of exploring the last 400m of the drift is due for completion by Christmas.''
Dr Smith said the work would only be slowed by setting up a new agency, as proposed with the other political parties.
"It is a hollow political stunt for parties to promise manned re-entry of the mine by the end of 2018. A political statement does not change the risks in the mine,'' Dr Smith said.
"This political commitment of manned entry of the complete drift by the end of 2018 could not be done under New Zealand's workplace law - a law supported by these very parties.
"They are either making empty promises to the Pike families or are proposing to water down a law intended to prevent future workplace tragedies.''
- By Laura Mills of the Greymouth Star