The mother of a 21-year-old who died in the Pike River Mine says it is a "wonderful day" now that a reentry date is set.

Pike River Re-entry minister Andrew Little has announced they'll be re-entering the mine drift on the third of May.

After a bit of delay the day, which the loved ones of the 29 men who perished at the mine in 2010 have been waiting so long for, will be marked with an event on the West Coast attended by Little, Prime Minister Jacinda Ardern and Deputy Prime Minister Winston Peters.

When Little announced the plan to re-enter the mine in November last year, he hoped the work to breach the 30m seal inside the drift would begin in February.

Sonya Rockhouse, who lost her son Ben in the tragedy, told Larry Williams it's wonderful news.

She says they were told about it last night, but to actually hear the announcement was wonderful. 

Her other son, Daniel, survived, and she says she's not giving up hope bodies or body parts might be found. 

"Daniel was knocked out for 50 minutes and then took an hour and 25 minutes to get out, so it's highly possible that somebody else, one, maybe more, could be in the same position. Knocked unconscious, came to, and tried to get out."

She does not agree that there won't be any bodies in there, and has "very high" expectations that something will be found. 

"I think it's highly possible that there might be some bodies in the top end of the drift." 

Rockhouse also hopes they might find the remnants of the driftrunner, which took men in and out of the mine.

She is confident that some sort of physical or electrical evidence will be found to show the cause of the explosion. 

"Whatever that evidence that is, I believe they will find it."

Breaking through the 30m seal in the Pike River mine drift on May 3 will really herald the beginning of re-entry, Pike River Re-entry Minister Andrew Little says.

Little said today there had already been a huge amount of work already done to prepare for re-entry.

He told Larry Williams that there is still a And there was still more to do, including awaiting equipment from Australia.

"Once that's broken through, then the real project of re-entering the drift can begin."

He confidently predicts they will be in the drift by May 3rd, but it could take weeks or months to get to the other end. 

"Nobody's been in there for some years, so we don't know what the actual surface will be like. IOf there are areas where there is rockfall, the roof will have to be bolted. If they have to stop and retrieve equipment or human remains, they will have to stop." 

Little echoes Rockhouse's thoughts that because two of the miners were able to get out, there might be others who nearly made it out of the mine. 

"There is a chance, only a small chance, that others got far enough up the drift before they succumbed. That is a possibility." 

He says that there will most likely be some physical evidence that they can retrieve. 

Worksafe had been reviewing all aspects of the planning, risk assessments and supporting documentation to ensure the re-entry plan was safe, he said.

It is hoped that work in the drift will enable the agency and police to investigate what caused the explosion that killed 29 men on November 19, 2010.

Little said how long it took to get into the mine depended on the progress the team made in the early weeks.

"You've got to remember that drift, that tunnel, runs uphill so it will be a pretty arduous task. You're looking at 40 metres by 40 metres at a time."

There were no plans to go beyond the rockfall. The plan would include recovering part of the drift known as the pit bottom in stone.

"It will be up to them, once they get in there, to work out the pace that they can do so safely," Little said.

He says if they make it that far, there will be very useful equipment in that area that will give an area of what happened.