Germany's 'Reichsbuerger' coup suspects go on trial

Nine men are set to go on trial in Germany charged with high treason, attempted murder and plotting a violent coup d'etat aimed at installing an aristocrat as national leader and imposing martial law.

The hearing in a maximum security courtroom in Stuttgart marks the start of three marathon trials of 27 people in total accused of conspiring in a plot foiled by authorities at the end of 2022.

Together they amount to one of the largest legal proceedings in German history.

Monday's trial focuses on nine suspects, members of the Reichsbuerger (Citizens of the Reich) group, who allegedly aimed to impose harsh military law on Germany after carrying out a coup.

The country's domestic intelligence service Verfassungsschutz put the Reichsbuergers, who it says number some 21,000 people and who do not recognise modern-day Germany as a legitimate state, under observation in 2016.

The political leadership of the group on trial, led by real estate investor Heinrich XIII Prinz Reuss - scion of a now throneless dynasty - appear in court in Frankfurt next month, while another group of suspects including an astrologer stand trial in June in Munich.

Prosecutors say that the suspects' meticulous planning and stocks of firearms and cash show they were a real danger.

"They planned to infiltrate an armed group into the parliament building in Berlin, detain legislators and bring down the system," they wrote. "They understood that seizing power would involve killing people."

One of those going on trial on Monday, referred to in trial documents as Markus L, shot and seriously injured a policeman while resisting arrest, prosecutors say.

The nine had stored up 500,000 euros ($A820,000) in cash alongside 380 guns, 350 bladed weapons and some 148,000 rounds of ammunition.

Reichsbuergers tend to believe they are citizens of an earlier Germany - typically the pre-World War I German Reich - which has been usurped by today's federal republic.

They base their beliefs on the idea that a foreign "Alliance" including the US and Russia stands ready to help them depose an illegitimate "Deep State" squatting in office in Germany since World War II.

"These militant Reichsbuerger are driven by hatred for our democracy," interior minister Nancy Faeser said on Sunday. "We will continue our crackdown until these militant structures have been fully exposed and crushed."

The Reichsbuergers have parallels to and are partially inspired by similar sovereign citizen or the QAnon movements in Britain and the US, where theories about a Deep State helped fuel the January 6, 2021 storming of the Capitol in Washington DC.