It is believed an automated messaging system was hacked and the evacuation message was sent to landline phones in the Maitland area.

The message falsely advised people that a number of schools in the area had been evacuated, which caused some hysteria online and in the city.

It took some time for the SES and police to find the source of the panic.

When the hack was discovered NSW Police released a warning about the message, which is the subject of an investigation.

NSW SES deputy regional incident controller Andrew Galvin said residents needed to be vigilant when it came to emergency announcements.

“It is not just the malicious message, it was other rumours that were circulated by the community on Facebook,” he said.

“It is important to understand where information is sourced from. 

“Anyone posting or sharing information should look to verify it first.”

Mr Galvin said residents should look to the SES, police and emergency services for reliable information, especially in times of crisis.