Later, he saw the smashed glass.
The vehicle did not stop until it hit the branch's back wall, which it also damaged.
Forensic officers spent hours going over the vehicle as it remained inside, surrounded by smashed furniture and shattered glass.
Nobody was in the bank when emergency services arrived.
Debris was strewn all around the interior.
A ute which smashed spectacularly through the glass doors of a bank in Perth's CBD on Christmas Day has been removed from the scene as police investigate whether it was a deliberate act.
The witness, who did not want to be identified, said he thought the driver of the utility was a man.
"It was a deliberate act," he said.
A man who was driving on St Georges Terrace told the ABC he saw the vehicle coming up the Terrace from the east, before mounting the verge and lining up in front of the bank.
Emergency crews were called to the corner of St Georges Terrace and William Street just before 4.30pm on Friday following reports of a car crash.
In Mount Lawley, a woman was charged with a string of offences, including driving under the influence and having no authority to drive, after she was spotted driving recklessly in a Holden Barina along Walcott Street early on Christmas morning.
Police are investigating after a driver smashed into the bank offices of Westpac in the Perth CBD on Christmas Day and fled the scene after causing significant structural damage to the building.
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