A number of police officers are also assisting with traffic on nearby streets.
Fire crews were now looking for any hotspots. They were also making sure no cars had been affected in the carpark area of the building.
"With the carpark above [the building] it was pretty hard to ascertain how many people were driving in there, parking and moving around," Shaw said.
"One we arrived our priority was to evacuate the building."
Shaw said there were no reported injuries at this stage.
He could not specify how many people were evacuated from the plaza but said given it was during the afternoon in the busy area of Newmarket, there were likely to have been a large number involved.
Juliette Veber was on Kent St and could see "grey billowy smoke" coming from the second story of the Newmarket Plaza foodcourt.
"I just saw smoke billowing out of the top of the carpark on top of the food court. It smells really smoky, everyone is outside watching."
One firefighter was in a cherrypicker being raised to the smoke's level, she said.