Students have been allowed back to some sections of a Cairns high school after police made an emergency declaration under the Public Safety Preservation Act (PSPA) following an ongoing incident.Emergency services were called to the scene after 9:25am following reports of a threat and students, as well as those in surrounding buildings, were evacuated.Police said nothing suspicious had been found and revoked the PSPA declaration about 11:20am.Residents were being allowed to return to the surrounding areas.Police had earlier told parents and carers not to attend the facility to collect their children while the incident was ongoing.An exclusion zone was set up between Lake Street, Minnie Street, Grove Street and McLeod Street.Residents had been urged to remain indoors and to avoid the area.