By evening, Mr Bush - now Police Commissioner, then a detective inspector and New Zealand's police liaison officer in Thailand - had traded his Bangkok family home and office for a disaster zone.
He barely slept in the seven days that followed.
The Thai authorities had set up a base in Phuket town. Mr Bush, as New Zealand's representative on the ground, recalls standing, waiting in the huge, largely empty hall that would become the central point for those who needed help.
Dozens of others stood behind tables bearing the flags of the country they served. He did too.
Then the doors were unlocked.
"Hundreds of distraught people came through the doors. They'd lost their families, their kids, their possessions. The absolute outpourings of grief ... "
The sheer press of those seeking help was overwhelming. And that was the next 18 hours consumed until help arrived.
Mr Bush left to tour the area, compiling reports for those back in New Zealand trying to measure the scale of the disaster.
Police contacts helped with transport and other logistics as he moved over the course of days from Phuket to the "utter devastation" of Khao Lak, 88km to the north, where more than 4000 people lost their lives.
"It was actually three to four days before you really realised the impact of the tsunami. It was when I got to Khao Lak."
The flat landscape had nothing to resist the force of water rushing in from the sea. It withdrew, leaving wreckage and the dead in its wake.
Bodies had been gathered to lie outside temples in the humid open air, awaiting whatever step came next. Mr Bush counted 300 people at one temple, 600 at the next.
"The thing that does affect you is seeing the victims, and the victims' families ... and on your travels seeing the deceased, the huge number of children who had perished."
The knowledge he earned fed a need back in New Zealand - it allowed Mr Bush to relay estimates of a Kiwi death toll far lower and more accurate than that touted in the media.
"On the first day, you were expecting a lot more," he said.
It also armed him with details needed locally. The Thai authorities emerged as open to advice, and heard from Mr Bush a recommendation to shift victim identification from a health-led effort to one overseen by police.
In the days following, international police teams, including from New Zealand, began the task of matching the names of those missing to the bodies of those found.
Mr Bush retreated - for a day - to Bangkok, back from the "intensity" of a week in which he rarely slept.
And then he returned. And returned - back for work, back for the one-year memorial, back this year for the 10-year commemoration.
Even a year after the tsunami, hotels had been rebuilt, gardens landscaped and tourists returned.
"You wouldn't think it had happened," Mr Bush says.
It might not have scarred the landscape but, he says, "it would be hard to find a more significant event in your life".
Kiwi victims
The five New Zealanders killed in the Boxing Day Tsunami were:
•Andrew, 42, and Belinda, 26, Welch
•Leone Cosens, 51
•Craig Baxter, 37
•Stephen Bond, 46
