An Islamist preacher who allegedly led "Sharia police" patrols in the western German city of Wuppertal is standing trial on charges of supporting a terror organisation in Syria.

Muslim convert Lau, 35, is accused of supporting Jaish al-Muhajireen wal-Ansar (JAMWA), a group of foreign Islamist fighters operating in Syria.

His trial is due to begin today (6 September) in Duesseldorf, DPA reported. According to the agency, prosecutors may seek to charge Lau as a terrorist.

Lau is one of the most notorious figures in Germany's hardline Salafist subculture.

In 2013, Lau allegedly drove two Islamists to Syria to join JAMWA, which subsequently split into factions supporting al Qaeda's Syrian branch and Islamic State (Isis/Daesh).

Lau is also accused of providing the group with night-vision goggles and money.

The following year he was accused of leading "Sharia patrols" of extremists who attempted to impose a hardline interpretation of Islamic law in the city of Wuppertal.

Dressed in orange high-visibility jackets, the group ordered people outside nightclubs to stop drinking and listening to music, and declared gambling prohibited.

In a controversial ruling, a court decided that the jackets did not breach German rules banning groups adopting their own uniforms in public, and the gang did not face prosecution for preaching hardline Islamist doctrine on the streets.

Lau's trial is expected to last until January, 2017.