Sydney teen arrested over death threats to Christians

Mounted police are seen patrolling the streets in downtown Sydney amid heightened security. Photo / AFP

A second teenager has been charged after death threats were allegedly screamed at Christians outside a school in Sydney's west.

A 14-year-old was in the front passenger seat of a red hatchback when he allegedly began yelling abuse outside the Maronite College of the Holy Family in Harris Park on September 16.

Onlookers told AAP the boy and the car's driver threatened to "kill the Christians" and slaughter their children while brandishing an Islamic State flag out the window.

Police said an 18-year-old was arrested on Wednesday evening, and had been charged with intimidating a school staff member and behaving in an offensive manner.

The man, who was a juvenile at the time of the incident, was granted conditional bail to appear in a children's court on October 20.

A 14-year-old boy was arrested by police on Tuesday and will appear in a children's court on October 13 on the same charges.

Meanwhile Victoria Police Chief Commissioner Ken Lay has urged his officers to be cautious and alert following an attack from a terrorist suspect who was shot dead.

But Victorians have been told to stay calm, and Premier Denis Napthine insists the incident was the actions of a individual.

Numan Haider, 18, was fatally shot outside Endeavour Hills police station after allegedly attacking two officers on Tuesday night.

Police say the officer had no other choice after Mr Haider had repeatedly stabbed an Australian Federal Police officer and the leading senior constable who shot him.

Mr Lay has written to the state's police officers and asked them to exercise extreme caution and remain vigilant.

"This has been a confronting reminder to all police members about the stark realities and dangers that can present themselves at a moment's notice," he said.

Mr Lay said counter-terrorism officers had been aware of Mr Haider for about three months, and had invited him to the police station after becoming concerned about his behaviour.

Mr Haider, of Narre Warren, had been seen at a shopping centre displaying a flag linked with jihadist group Islamic State, or ISIL, and last week had his passport cancelled on national security grounds.

- AAP