SYDNEY, Australia — Five teenagers brandishing baseball bats and machetes rampaged through a suburban school today and hit a teacher over the head, police said. Eighteen students were treated for minor injuries.

The drama unfolded as hundreds attended an assembly in an outdoor area of Merrylands High School. As the attackers moved in, teachers rushed the students back to class, where they sought refuge behind locked doors, under desks, even in a cupboard.

"I find it very difficult to believe the brazenness of how they entered the school," Police Detective Inspector Jim Stewart said. Such school violence is rare in Australia.

The teens, between the ages of 14 and 16, were arrested and likely would be charged with assault and other crimes, Stewart said.

Police refused to say whether the teens were students at the school. They were still being questioned by police late today.

A 43-year-old teacher was treated at a hospital after being hit on the head with a bat when he tried to stop the attackers, and 18 students were treated for cuts from broken glass and other minor injuries, Stewart said.

Two of those students — a 13-year-old boy and a 14-year-old girl — were taken to a hospital for further treatment, police said. No one was seriously injured, Stewart said.

Some students reported the gang was armed with two machetes.