"We won't be making a statement. We will find out what went wrong and deal with it appropriately. We don't make a statement on every accident," Ritchie said.
The police commercial vehicle safety team is also investigating the accident.
A police spokeswoman said initial inquiries suggested the accident was possibly a simple mishap.
Yesterday, Ritchie said the bus was on a timetabled route.
"It seems a bit of a strange one. We'll get the vehicle back and have a look at it this afternoon. We've got to treat it seriously, it could have been disastrous."
Ritchie said his main priority was the safety of the people on board. He confirmed the female driver was okay and said some of the passengers walked away from the crash.
The crash brought down powerlines, Fire and Emergency NZ spokeswoman Megan Ruru said.
Ben Scanlan, who lives across the street, was making breakfast went the crash happened.
"It sounded like a big clap of thunder," he said.
"The house shook."
Ambulance services were on the scene within minutes, he said.
Barbara Senior, who lived in the block of flats, felt the crash and went outside to investigate.
She comforted one passenger and gave the person a drink of water.
"They wouldn't come inside out of the wind. There was a man injured and there were ambulances but there were so many people offering help I just came in because there were so many people gawping."
Senior said the crash could have been far more serious.
"It's a very busy corner on a Saturday morning. Nobody seems to know exactly what happened. It's quite a strange place to come down the bank and past the letterboxes."