With six prison officers ambushed by thugs while escorting a high-risk inmate to court, five fellow officers run towards two stationary vans to try to rescue them.

Their red helmets glinting under the sun, the five officers take out the aggressors by firing shots at them. They save their colleagues.

But the "ambushed officers" were actually dummies and the "aggressors" were just boards.

The action that unfolded yesterday at the Changi Prison Complex was no prison break but part of a challenge involving local and overseas teams.

The officers were taking part in the five-day Asian Prisons Lockdown Challenge (APLC), in a new Operation "Man-down" event, which simulates an attack.

The challenge pits local and overseas correctional agencies in a friendly competition of tactical skills and expertise, testing them in mentally and physically challenging scenarios. Officers also shared their best operational practices.

The competitive phase of the challenge ended yesterday, with the team from the Singapore Prisons Emergency Action Response (Spear) Force - an elite prisons team trained to handle emergency security breaches and unrest - emerging as overall champion.

A team from Thailand was second, while a Macau one was third.

"APLC is a reminder for us that we must always stay competent to be able to react to any prison emergencies," said Superintendent of Prisons Ang Kien Tiong, chairman of the challenge's organising committee this year.

This means being prepared to deal with prison riots, although these have not happened here before. "The scenario is designed to (be) based as close to our operational situation as possible," he added.

Nearly 50 officers from the Singapore Prison Service, Macau Correctional Services Bureau and Department of Corrections Thailand took part in the fourth edition of the biennial event this year.

About 250 representatives from the correctional agencies of six countries have taken part in the challenge since its inception in 2010. The challenge is organised by the Singapore Prison Service for its regional counterparts.

Officers were put through individual and team events, including one where they had to search for casualties in a barricaded environment of mock-up prison cells.

Spear's Staff Sergeant Cleve Mu, 33, who has participated in all four editions of the challenge, said it gets more challenging each year, and more realistic.

This helps in their improvisation and teamwork, he said, as officers need to be able to strategise in the face of unexpected situations.