A local reporter for ABC 6 in Columbus spoke with an eyewitness who refused to go on camera but described how the attack began:
The eyewitness tells ABC 6 that the fire alarm was pulled in the Watts building in the stairwell. Everyone then evacuated and the fire department came to investigate.
It was when the all-clear was given that a car pulled up, potentially running into people, and a man got out wielding a machete (or large knife) and began attacking people.
I would note that CNN is reporting that the feds are saying the attacker mainly used his car and a machete (knife):
JUST IN: Suspect in Ohio State attack predominately used a knife and car, federal law enforcement official says https://t.co/USGIbJJUx8
— CNN (@CNN) November 28, 2016
This also confirms a similar report from earlier:
Witness tells NBC4 that a fire alarm was pulled, people cleared Watts Hall, then a car came along and started hitting those who evacuated.
— Matt Edwards (@MattEdwardsNBC4) November 28, 2016