WATCH: World's biggest disaster simulation takes place in Portsmouth

Outside dozens of firefighters pour out of a fleet of fire engines, rushing to secure the gaping holes that scar the side of the two-storey block following a huge storm.

Some of the men immediately begin treating casualties on the floor outside while others clamber through exposed brickwork to reach those injured inside.

Opposite, paramedics with large backpacks step onto an aerial ladder platform to reach the top floor of a three-storey building, where wounded schoolchildren are trapped.

This is the frenetic scene from the opening day of the globe’s biggest international disaster simulation exercise – one based in Portsmouth.

Known as Simex, the operation involves more than 3,000 people from 64 emergency response organisations spread across the UK, as well as more than 900 role players.

It’s designed to put all these services to the test in the event of a major disaster.

This year’s three-day exercise will see crews dealing with the aftermath of a hurricane that has ravaged the area, with heavy winds blitzing buildings and storm surges flooding coastal and inland areas.

Naomi Morris, a lecturer in humanitarian emergency response and recovery at the University of Portsmouth, and secretariat to the Simulations and Training Network of the United Nations, is the event’s co-director.

Speaking of the drill, she said: ‘There has been large-scale destruction, buildings have collapsed, there are displaced people.

‘In addition, an oil tanker has unfortunately had an accident and there’s oil everywhere.

‘You’ve got response from environmental teams, medical teams, and search and rescue teams. It’s huge.’

Almost 200 casualties were spread across Eastney’s Fraser Range and in Langstone, where dozens of people needed to be rescued from the water.

In the derelict buildings of Fraser, dozens of children from St Swithun’s Catholic Primary School alongside university students and teachers, needed to be saved.

Year 5 St Swithun’s pupil, Izzy Fawehinmi, nine, of Portsmouth, was one of them. She said: ‘I was feeling a bit nervous and excited about today.

‘I was supposed to have been hit with something during the storm so I’m going to scream and cry and be very dramatic. It’s been fun so far.’

Classmate Oscar Newland, 10, added: ‘This is my first time doing anything like this so I was a bit nervous.

‘But there’s a lot of people around so you know you’re safe.

‘It’s a great experience.’

Laura Martin, 34, is a second year nursing student at the University of Portsmouth. She was playing a dead casualty.

She said: ‘It does feel realistic and it’s exciting. This is the second time I’ve been involved.

‘It’s amazing how well everyone comes together.’

Simex started in 2012. It is taking place across 18 sites in Hampshire this year.

Other scenarios include rescuing people trapped in tunnels, clearing up an oil spill and dealing with a refugees fleeing the storm-hit area.

Phil Crook, the fire service’s specialist technical rescue team section leader, said: ‘Hampshire Fire and Rescue Service is among the best in the country and we are regularly called upon to help in the aftermath of international disasters.

‘Exercises like this are vital in developing and maintaining our skills and getting valuable experience working alongside our partners.’

Simex continues until tomorrow.

It is arranged by the university, Hampshire fire service, RedR and L2S2.