Dutch appeals judges on Monday ordered the continuation of anti-Islam lawmaker's Geert Wilders' hate speech trial, rejecting his claim that the court trying him was biased.

Wilders is on trial on charges of "making statements insulting to Muslims as a group," and inciting hatred against Muslims.

Presiding judge Marcel van Oosten rebuffed defence calls for the case to be dropped, saying "his right to presumption of innocence has not been violated."

He said a judge who discussed the case with a witness at a dinner party had not attempted to tamper with the witness and the court's independence had been demonstrated.

One of Europe's most prominent right-wing populists, Wilders argues that his remarks comparing Islam to Nazism and calling for a ban on the Quran are part of legitimate public debate that is protected by freedom of speech.

Muslim groups say Wilders is infringing their right to freedom of religion by increasing discrimination against them.

Wilders' case, seen as an important test of the limits of freedom of speech in criticizing minority groups, has turned into a two-year odyssey that has included the scrapping of a panel of judges for the appearance of bias.

In the meantime his popularity and political influence has grown, with many of his ideas — including further restrictions on immigration — adopted by the current conservative government in return for his support.

Wilders showed no emotion as Monday's decision was read. He waved briefly to supporters before leaving the courtroom for a break.

The trial then recommenced from the beginning — in an abridged form — with a reading of a selection of Wilders' remarks and the showing of his short film Fitna, which argues Islam is by nature a violent religion. Its release in 2008 led to protests in many Muslim countries.

A verdict is expected in mid-June, but no date has yet been fixed.