Russia news agencies quoted the Moscow region's health ministry as saying that a 45-year-old man and a 40-year-old woman have been taken to the hospital from the Moscow Regional Court with gunshot wounds. As per reports, at least three people lost their lives.
The agencies earlier quoted a lawyer who was at the courthouse and saw a guard and a court official injured.
Authorities said the incident took place during a hearing in a case of a gang of nine people who are suspected of killing more than a dozen of motorists.
Russia media dubbed the accused "the Grand Theft Auto gang" after the violent video game. The men on trial are accused of terrorising Moscow motorists for months in 2014.
Prosecutors said the gang members were placing spikes on roads, forcing the motorists out of their vehicles and shooting them dead.
The nine men, all from Central Asia, are charged with 17 murders and two attempted murders.