Mr Walker said an initial look at the wreck suggested a cable the helicopter was using for lifting played a key role in the crash.
"There's certainly some clues that lead us to believe there was an issue with the cable that was being used... and that it interfered with the helicopter.
''[The pilot] was lucky to walk away from this.''
The CAA said live footage of the crash taken by a TVNZ crew would be very helpful in finding the cause of the grounding.
A preliminary report was expected within four weeks.
One witness, Richard, was using binoculars to try to work out what the helicopter was doing when the drama unfolded before his eyes.
The helicopter had appeared to be about 5m from the ground when something snapped and it plunged.
"The scary thing was actually seeing everyone on the ground running for their lives,'' he told APNZ.
"People started running away and then they started running back (to help the pilot).''
They wrenched the helicopter door open and helped him from the wreckage, Richard said.
Most of those involved were wearing hi-visibility vests and Richard believed they were probably involved in the operation.
It was a surreal feeling to be out of danger but watching it unfold before his eyes, he said.
"The nice thing is I wasn't looking at someone's leg being chopped off.''
The area was often busy at that time of the morning but wasn't today.
"If it was lunch time it could have been really nasty.''
Kyle Geddis said he heard the helicopter hovering and then a loud bang.
He then headed towards the bridge and called emergency services on the way.
Another witness, Jason Aarsen, was sitting down for a break at the waterfront and was watching the chopper extend a black ladder by lifting up an attached cable.
"I hear a massive whack of two power cables hitting each other and as I turned around, I just saw the helicopter drop, completely freefall,'' he said.
"The blades blew out and completely freefalled down, snapped in half.''
"It propped itself up and sat like a fish out of water. It was really gnarly.''
"The pilot was sitting there, speaking''.
Mr Gribble who runs family business Helisika Helicopters, is in his mid 50s and has been flying "for years'', daughter Jade Gribble said.
Ms Gribble - who is nine months' pregnant with her first baby - was manning the phones at Helisika Helicopters when news of the crash came in.
"I know that he's walked away,'' she told APNZ.
"I know that he's on his way to Auckland Hospital.
"I'd say he's very, very lucky to walk away.''
Son Jaz Gribble, who also flies for Helisika, said he was filled with shock and relief when he heard of his father's miracle escape. "Someone must have been looking out for him. That's all we could have prayed for - that he's safe and happy. Someone must have been on his side.''
Jaz Gribble was flying and found out about the crash when he landed after 11am.
He was rushing to hospital to see his father and not looking forward to viewing footage of the crash.
"He's my dad, so it's a little close to the bone for a start. This has shaken me.''
Mr Gribble said his father was an experienced pilot who had been looking forward to the "special job'' of erecting the Telecom Christmas tree.
Early reports he received from ground crew were that a cable had caught in the helicopter rotors and caused it to come crashing down.
"Something must have gone horribly wrong. That shouldn't have happened.''
Fire Service assistant area commander Paul Turner said Mr Gribble told emergency services the helicopter was winching a ladder into place when something went wrong.
Neither the pilot nor the single ground crew knew what happened.
It was now up to police and Civil Aviation Authority (CAA) to remove the wreckage.
Transport Accident Investigation Commission spokesman Peter Northcote said it would be leaving the investigation to the CAA.
Telecom spokeswoman Catherine Murphy, who saw the crash, said the company had checked with Mr Gribble to make sure he was OK and then "left him to it''.
They would be in touch with him once he had been treated and had time to deal with what had happened.
The area was closed to the public at the time, she said.
