Police are searching for the male colleague of a young woman who was found dead in a school in Sydney's CBD with severe head injuries.
Just minutes before midnight, emergency services were called to St Andrew's Cathedral School on Kent Street.
Police found the body of 21-year-old water polo coach Lilie James in the toilet area of a gymnasium at the school.
Officers are currently searching for Paul Thijssen, a male colleague who was working at the school as a sports assistant.
NSW Police Superintendent Martin Fileman said the scene was "confronting" for the officers who found James, who was the victim of an "apparent" homicide.
"Last night police from Sydney city police area command were responding to a welfare check and attended the school at St Andrew's cathedral where police located the body of a female in her early 20s in the gym area of the school," he said.
"From her injuries, it was apparent she was a victim of a homicide."
Investigators are seeking to speak with Thijssen, also in his 20s.
He and James were known to each other, Fileman said, but there was no police history of domestic violence between the pair.
A second crime scene has been established at Vaucluse, where police believe they have discovered "property associated with the homicide was located".
Police are combing the reserve and are patrolling the waters off South Head.
Fileman said police were interviewing several people, and that other staff were present in the building at that time.
The school issued a statement confirming it would remain closed today to everybody except those sitting Year 12 exams "following an onsite death overnight".
"No students were involved and there is no ongoing threat," a school spokesperson said.
"An area of the school, not accessible to students, is a crime zone, and we await the approval of police before bringing everyone back on site."
School counsellors have been called in to offer support for parents and students.
"The only students onsite are those sitting exams, and we ask that the media does not seek to interrupt their concentration or state of mind as they sit exams that are significant for their graduation," the spokesperson said.
They said the school would not make any further comment.
One of Sydney's oldest schools, St Andrew's has fees ranging from $22,000 for kindergarten to $38,000 for Year 12.
Crisis support is available from Lifeline on 13 11 14.