Donning gas masks and grey chemical agent suits, Singapore Civil Defence Force (SCDF) officers ran into the bleachers at the Marina Bay Floating Platform just before 2am to evacuate "parade-goers" and "casualties" in the aftermath of a "chemical attack".

As the "injured" people were carried out of the venue in stretchers, the SCDF's Hazardous Materials (HazMat) team - wearing orange full-coverage suits - trooped in.

Their mission: to locate and dispose of a "harmful chemical agent" that had been hidden among rows of seats. With the help of HazMat detectors, the team managed to zoom in on a bag which contained the harmful source and disposed of it in less than 10 minutes.

But this hive of activity, with flashes of red and blue lights in the early morning on Tuesday, will not be part of the show performance at this year's National Day Parade (NDP), that will be hosted at the venue on Thursday.

It was an SCDF operational exercise to prepare emergency personnel for contingencies, should they arise during NDP.

It was the first time in recent years that the SCDF gave the media an inside look into their preparations for such major events, like the NDP and Singapore's Formula One (F1) race.

Speaking to the media after the exercise, which ended around 3am, SCDF's director of operations, Assistant Commissioner (AC) Daniel Seet, said major exercises like this gave officers the chance to familiarise themselves with the environment in case of a real incident.

He added that the exercise was a chance for personnel from the different agencies involved - the SCDF, Singapore Police Force, Singapore Armed Forces (SAF) and the Ministry of Health (MOH) - to work together and coordinate various parts of the contingency plan.

Just outside the floating platform, "casualties" were taken through the decontamination process during the operational exercise, where their clothes were removed and they were tended to at four decontamination vehicles.

Once the "injured" victims were clean, they were taken to the first-aid point at the F1 Pit Building, where the SAF and MOH provided medical assistance.

Said the SCDF's AC Seet of the four-agency operations: "The entire chain is very important and no part of the chain can fail."

The exercise involved a total of 400 personnel and 55 vehicles from the four agencies.

The Singapore Police Force will also form part of the 5,600 personnel in the security operations for this year's NDP celebrations.

Officers will be deployed from various units, such as the Traffic Police, Police Coast Guard, Gurkha Contingent and the Special Operations Command's K9 unit.

The In-Situ Response Teams (IRTs), with their distinctive beige berets, will make their NDP debut this year. These teams will be deployed at shopping malls in and around the Marina Bay area, and will be very visible to the public during their patrols to deter any terrorist attack. The IRTs comprise mainly full-time national servicemen who are specially selected, trained and armed to deal with public security incidents.

Formed in December last year, the teams have been deployed in areas with high footfall, like Orchard Road and Marina Bay, to enhance security during festive periods.

The teams will complement existing security forces deployed for NDP like the Emergency Response Teams (ERTs). But the IRTs' focus is more specific because of the high footfall areas they patrol, while the ERTs cover a wider area.

The IRTs are also likely to be the first responders in the event of an attack.