As angry anti-racism protesters rallied outside the courthouse Monday, the woman at the centre of a landmark German neo-Nazi murder trial was the picture of calm.

As Beate Zschaepe entered the courtroom, arms casually crossed and looking confident, she briefly glanced toward the television cameras, then turned her back on them.

The 38-year-old -- best known to the public looking dishevelled in a 2011 police mugshot -- now sported a black pantsuit, pressed white shirt, earrings and a glossy new hairstyle.

While demonstrators outside noisily demanded justice, she chatted with her defence team, drank a glass of water and took a piece of chewing gum from one of the lawyers.

While Zschaepe projected calm, emotions frayed on the street over the self-styled National Socialist Underground (NSU), a trio accused of 10 execution-style shootings between 2000 and 2007.

Relatives of many of the victims -- eight of the dead had Turkish roots, one was a migrant from Greece -- had arrived by bus, including Ismail Yozgat whose 21-year-old son died in his arms after being shot twice in the head.

"How could they kill so many?" read a banner held up by ethnic Turkish protesters. Others read: "Together in the battle against racism" and "Opportunity for justice".

In a brief scuffle, two young women broke free from the demonstration, smashed a bottle on the street and rushed toward the court before they were held back by police.

Security services were taking no chances for the trial, fearing pro- and anti-neo-Nazi violence.

Police deployed 500 officers plus private security guards, had sealed off the perimeter earlier and banned cars and even bicycles from parking in the area.

The trial, Germany's biggest anti-terrorism case since members of the left-wing Red Army Faction were in the dock in the 1970s, is expected to last well into 2014.

In all, 80 victims and relatives of those killed, represented by about 60 lawyers, will join in the trial, as will 600 witnesses.

Zschaepe, who was taken to court in an armoured black car but wore no handcuffs in court, is the main defendant accused over conspiracy to commit the murders and terrorism and arson charges.

Four co-defendants face charges of having supported the NSU. Two of the men guarding themselves with sunglasses and a paper folder as they walked into a hailstorm of photographers' flashes.

The mammoth proceedings are being held in a courtroom with only 50 seats for the media and 50 for members of the public, most of which were also taken by journalists on Monday.

The first citizen to queue up for one of the public seats was 68-year-old pensioner Helmut Sieber, who had arrived on Sunday, more than 20 hours before the start of the trial.

Asked why he came so early, he told AFP: "I don't want to give the Nazis an opportunity to get inside."