Five teenage boys brandishing machetes and baseball bats have left a trail of destruction and injuries in their wake, after storming a western Sydney high school, police say.
The terrifying rampage through Merrylands High School left 18 students and one teacher injured and may have been motivated by revenge, police said.
Teachers immediately locked down the school when the armed group confronted the school body during assembly at about 8.50am (AEST) Monday.
Students were ushered to classrooms, some hiding under tables and in cupboards while their teachers barricaded the doors.
Parents, police and the NSW Department of Education praised staff for their quick actions to protect students as the five youths allegedly ran through the corridors of two school buildings, smashing every window they could find and showering students with glass.
"They were carrying baseball bats and two had machetes. I thought I was going to die," a Year 12 student told News Ltd.
"Teachers just told us to get down. Students were just crying and screaming."
The five boys, aged between 14 and 16, were arrested just six minutes after entering the school, the education department said.
Police said they dropped their weapons when confronted by officers and did not resist arrest.
Late Monday, the teenagers were still being questioned by police but could face charges of assault, affray and malicious damage.
A 43-year-old male teacher was taken to Westmead Hospital as a precautionary measure after suffering bruising to the back of his head while trying to restrain one of the youths.
A total of 18 students were treated at the scene for injuries, mostly caused by the broken glass.
Two of those students, a 13-year-old boy and a 14-year-old girl, were taken to Westmead hospital for further treatment.
Detective Inspector Jim Stewart of Holroyd Police admitted being confounded by the attack.
"It beggars belief they would attempt this kind of activity against innocent students and the school," he said.
Asked if the attack was a revenge attack he said: "Possibly".
"The information to us is they were coming here ... seeking someone," Insp Stewart told Macquarie Radio.
One unnamed male student said the five teenagers had burst into the school looking for another student.
"We were having assembly, when a bunch of guys walked in with machetes and baseball bats, and they said they were looking for some kid," he told Network Ten.
Another boy said the students were petrified by the attack.
"I was scared," he told Network Ten.
"They (the students) were all hiding under tables, they were so petrified."
The unnamed mother of a Year 12 student said the "teachers were actually (barricading) the door".
"They showed the parents that they put their life on the line for the kids," she said.
NSW Department of Education director general Michael Coutts-Trotter praised the teachers, saying the school lockdown was part of a principal's training.
"I just want to recognise the principal at Merrylands, who is a fabulous school leader," he told Macquarie Radio.
"She leads a fabulous staff and they did a fantastic job today."
NSW Education Minister John Della Bosca said a "potential tragedy" had been averted by the teachers and police.
"The police and the teachers behaved in a very professional manner," he told Network Ten.
"They responded with their training ... they made sure that the students were as safe as they possibly could be."