An armed student on Monday briefly took 20 teenagers hostage in a Moscow school and killed a policeman and a teacher before being detained amid security jitters ahead of the Sochi Winter Olympic Games.

Police said a student armed with a gun forced a security guard to lead him to a specific classroom in the school on the northern outskirts of Moscow and then locked himself inside with about 20 teenage pupils and the class teacher.

He then opened fire through a window at scores of police who had rushed to the scene. Security officials said the student made no demands and did not conduct negotiations with officials during the broad daylight raid.

"He killed a policeman and wounded another," Russian interior ministry spokesman Andrei Pilipchuk told the state-run Vesti-24 news channel.

"He also killed the teacher."

The Russian interior ministry said the hostage-taker had been detained during a police raid on the school and that all the students were now safe and unharmed.

"None of the students have been harmed," Pilipchuk told Vesti 24. "They are all alive and well."

Police said the hostage-taker was one of the school's upper-class students but did not release his name. Schools in Russia usually house children from first to 11th grades.

Live footage showed a group of children running from the school and an emergencies ministry police helicopter hovering overhead.

Interior Minister Vladimir Kolokoltsev and Russia's powerful Investigative Committee chief Alexander Bastrykin both immediately rushed to the scene of a crisis that underscored the security problems facing Russia as it prepares to host the Winter Games in Sochi on Friday.

Security has been a prime concern for President Vladimir Putin -- his personal and political prestige linked closely to the Game's success -- because Sochi rests near the volatile North Caucasus region where Russia has been battling an Islamic insurgency for most of the past two decades.

Islamists who want to carve out their own state in southern Russia have vowed to stage deadly attacks during the Games that would undermine Putin and show that he lacks control over the vast country.

Russia has been on heightened alert ever since succesive-day late December suicide strikes in the southern Russian city of Volgograd killed 34 people at a railway station and on a trolleybus.

The attack was later claimed by two young men from Russia's North Caucasus in a video message that promised more attacks.

Security analysts believe that Sochi itself will be relatively safe both for athletes and visitors because of the extraordinary security precautions that have been taken at the Black Sea resort port.

Russia has deployed 37,000 security personnel around Sochi and is also patrolling the Black Sea for possible signs of an attack.

But analysts point out that the extra security measures being taken around the Olympic host city may leave other parts of the country exposed.

Many of the foreign visitors arriving for the Games will enter Russia through Moscow before traveling on to Sochi. (AFP)