TOKYO (REUTERS) - Tokyo held its first missile evacuation drill on Monday (Jan 22) with volunteers taking cover in subway stations and other underground spaces that would double as shelters for the Japanese capital in the event of a North Korean missile strike.

The choreographed evacuations at a fair ground and park ringing the Tokyo Dome baseball stadium involved around 300 volunteers.

Small groups of protesters scuffled with police as they demonstrated against what they criticised as a war game that fanned public fear.

While hope grows that North Korea's participation in next month's Winter Olympics in South Korea might help defuse tension in the region, Japan is escalating efforts to prepare its citizens for a possible war.

Tokyo believes the threat posed by Pyongyang's ballistic missile and nuclear weapons development is deepening.

"A missile from North Korea would arrive in less than 10 minutes and the first alert would come about three minutes after launch, which gives us only around five minutes to find shelter," Hiroyuku Suenaga, a Japanese government official, told volunteers after the Tokyo exercise.

Small Japanese towns and villages have conducted similar drills as North Korea has pushed ahead with its missile and nuclear weapons programmes.

North Korea conducted its most recent and biggest nuclear bomb test in September and has tested dozens of ballistic missiles. The latest missile test in November reached an altitude of about 4,475km and flew 950km, splashing into waters in Japan's exclusive economic zone.

Pyongyang says its weapons programmes are a necessary defence against a possible US invasion.

Amid public concern over the possibility of more missile launches, Japanese public broadcaster NHK issued a false launch alarm urging people to take shelter six days ago. That came days after a similar false alert caused panic across Hawaii.

"I am not that worried about North Korea, if something happened that would be frightening," said Hidenobu Kondo, one of the volunteer evacuees. However, the 50-year-old company employee said the drill would not be of much use in the event of real attack.

"If I was at work it might be easy to evacuate, but If I was outside somewhere it would be more difficult," Kondo said.

Japan's defences against a ballistic missile strike include Aegis destroyers in the Sea of Japan armed with interceptor missiles designed to destroy warheads in space. PAC-3 Patriot missile batteries represent a last line of defence against warheads that can plunge to their targets at several kilometres per second.

Japan has also decided to buy two land-based Aegis batteries and cruise missiles that could strike North Korean missile sites.