The day before he went down the mine for the first time, Joseph Dunbar celebrated his 17th birthday.

It was a day out shopping and having dinner with his mother, Pip Timms.

"We spent the whole day together," Ms Timms said yesterday. "It's going to be my best memory to live by. We were very close. He was my baby. He was my world."

Yesterday was supposed to be her only child's first day underground at the Pike River mine, but he was so excited about his new job that he convinced his boss to let him start on Friday.

He is now missing with 28 others after an explosion in the mine as little as an hour into that first shift.

Joseph and his mother had recently moved to Greymouth from Christchurch to make a fresh start, and working at the mine had become his goal.

"We moved here for Joseph, to give him a different life, a better life," said Ms Timms.

Joseph immediately wanted to work at the mine, but first he had to turn 17.

A family friend said he had even tried applying as an 18-year-old while he was still 16.

After months of waiting, Joseph finally celebrated his 17th birthday on Thursday.

"We went shopping, we ate KFC," Ms Timms told the Herald. "It was always his favourite. I bought him a paintball gun.

"We spent the whole day together. We went to one of the local restaurants. They do a real good roast. He loved his food, and that's what he wanted to do."

Despite friends wanting to celebrate with him, Joseph stayed home that evening to be with his mother and because he knew Friday would be his big day.

"His mates wanted him to go out that night, but he said, 'I'm staying in. I have work in the morning'. He was so chuffed."

The next day, Joseph went to Pike River, where Ms Timms' brother-in-law escorted him inside for a quick tour.

They came back out and the brother-in-law gave Joseph a thumbs-up before leaving.

Joseph, bubbling with enthusiasm, grinned from ear to ear and returned the thumbs-up before disappearing into the mine.

No one has heard from Joseph and the others underground since the blast.

"He wanted to do this for a very long time," Ms Timms said.

"It meant everything. He set himself a goal, and achieving that goal meant everything to him. It meant he was going to travel with the company, take him different places.

"He was absolutely stoked. He was excited, he was ecstatic."

Joseph had previously worked at a local supermarket, but working at the mine would give him an opportunity to have a career. He started as an offsider, with a view to becoming a driller in a year or two.

Ms Timms said her partner, Gary Campbell, "just knew that Joseph could do it".

"[Joseph] texted him and just said how thankful he was and grateful he was and he would not let him down."

Friends at school said Joseph was the class clown - and often got into a bit of trouble.

A family friend said Joseph had fallen in with the wrong crowd in Christchurch but was leaving all his problems behind with his commitment to working at Pike River.

Ms Timms said he "had to just grow up a little bit" before starting work. Her son was a funny, cheeky, kind, caring and loyal boy.

But now, she was left waiting for any news from the mine.

"It's pretty horrendous really. It's quite hard. You just keep going but you get exhausted and try to rest, but you can't because your mind is just going over everything."

Ms Timms said she had been able to get a short nap yesterday afternoon, but sleep did not come easily. She went to only some briefings by rescue authorities because they were too difficult.

The wait to begin the rescue bid had been frustrating, but she understood why.

"They can't just rush in there because, I know, right from the word go, I know how it works ... If the oxygen rushes in and it hits that methane, then bam, they're gone, another blast."