Three women and one man were assaulted and sustained serious but non-life threatening injuries at the Australian National University in Canberra on Friday morning, ACT Police's detective superintendent Ben Cartwright said at an afternoon press conference.
An 18-year-old Caucasian man has been taken into custody and is yet to be charged, Det Supt Cartwright said, adding there was no ongoing threat.
The alleged attacker was in a statistics class when he stood up at the back of the room and approached the female lecturer with a baseball bat, detective superintendent Cartwright said during the press conference.
Other students intervened, with one wrestling the bat from the alleged attacker, and restrained him with the help of campus security.
'Incredible bravery on their behalf. I believe one of the students has actually taken the baseball bat from the other student [who had the bat] and ran away. They then returned later to give it to the police,' detective superintendent Cartwright said.
Three students and a female lecturer were "seriously" hurt and all four are in Canberra hospital with one believed to have a broken arm.
'They appear to be defensive injuries, we believe to have a couple of broken bones, a broken arm, but I'm not sure who has got what injuries," Det Supt Cartwright said.
Police were unable to provide a reason for the attack was but are "not ruling out" any motive, including a racial motive. At least "some" of the hurt students were Asian, detective superintendent Cartwright said.
Police also said in a statement that the alleged attacker was not known to police or intelligence agencies.
The university's deputy vice-chancellor, Marnie Hughes Warrington, paid tribute to ANU's students, saying they displayed "remarkable bravery".
Support was thrown behind the university by Education Minister Simon Birmingham on Twitter.
ANU say they will step up security for Open Day but stress it was an "isolated" incident.
Students took to social media to express dismay at the attack.
"Holy crap that's so messed up," Jack Kennedy wrote on Facebook.
"Didn't think this type of stuff would happen at ANU let alone in Australia."
Alexander Vuong arrived on the scene shortly after the assaults.
A friend of his saw students and a lecturer attacked by a man wearing a hooded jumper.
"He saw a man attack a few other students with a baseball bat," Mr Vuong told Jolene Laverty in a video on Twitter.
