Major breakdowns in Singapore's metro system exposed serious flaws in the security-obsessed country's ability to respond to an emergency, the transport minister admitted Monday.

"The execution of emergency preparedness plans... ought to be significantly improved," Lui Tuck Yew, a former Singapore Navy chief, told parliament.

More than 200,000 commuters were stranded, many of them underground, during two major disruptions in December, damaging the city-state's reputation for efficiency and crisis management.

Metro operator SMRT's chief executive Saw Phaik Hwa resigned last week amid strong public criticism of the firm's handling of the breakdowns, but much of the criticism was also directed at the government.

Publicly listed SMRT's main investor is state investment agency Temasek Holdings.

"SMRT could have better handled the evacuation of passengers in the stalled trains to reduce the sense of distress and could have provided clearer and timelier information and instructions to the public," Lui said.

This left commuters "confused and apprehensive in already disordered circumstances," the transport minister said.

"These disruptions exposed gaps in emergency preparedness and crisis response and we need to do much better," he added.

Last month's disruptions were the worst since the metro was launched in 1987.

The worst breakdown, which took place on December 15, lasted up to seven hours, followed by a less severe stoppage two days later.

Singapore has a population of just over five million. Most are dependent on public transport because of the prohibitive cost of cars.

Military training is mandatory for young men, emergency drills are held regularly and officials repeatedly warn that the wealthy island, a staunch US ally, is a prime target for attacks by extremist groups in Southeast Asia.