Police have swarmed through an Islamic school in south-western Sydney after reports of an intruder threatening staff and students with a knife.

Officers were called to al-Faisal College in Minto on Thursday afternoon amid reports that an armed man had entered school grounds and was asking if it was a Muslim school.

Police said the man entered the school on Benham Road about 2.10pm, spoke to a female staff member and left a short time later. He was last seen on Kitson Road.

A crime scene was established.

Primary school students hid under their desks while those from the high school were gathered in a prayer hall as the school went into lockdown, one mother said.

