VIENNA (REUTERS) - Police in the Austrian city of Innsbruck are trying to identify a group of foreign men believed to have sexually assaulted 18 women during New Year's Eve celebrations, a spokesman said on Wednesday (Jan 4).

The women have reported that unidentified assailants had groped and tried to kiss them that evening as they stood in or near a crowded central square for a concert and fireworks display. Most described a group of five or six men, the police spokesman said.

In neighbouring Germany last year, hundreds of women were sexually assaulted and robbed at New Year's celebrations in Cologne and suspects were mainly of North African and Arab appearance. Police there said they prevented a repeat of this year by screening 650 mostly North African men on the night.

Anti-immigrant sentiment has boosted support for far-right parties in both Austria and Germany after both countries took in waves of migrants, many of them from the Middle East and North Africa, during Europe's migration crisis in 2015.

Witnesses in Innsbruck, a city in the Alps in western Austria, said the New Year's assailants were in their 20s or 30s and had dark complexions, but their nationality was not clear.

"It has definitely been proven that they are foreign," the spokesman for the police in the western province of Tyrol said, adding witnesses reported they spoke English or poor German.

"We are investigating. We have videos of poor quality but we are trying to make the best of them."

The assaults happened despite a police presence reinforced because of the Cologne assaults and last month's truck attack on a Christmas market in Berlin, the spokesman said.

Roughly 25,000 people gathered in the area of the central Market Square for a concert and fireworks display, visibility was limited, he added.

"We have never seen anything in this form," he said.

"I cannot remember (an attack) of this intensity, on this scale and with this modus operandi."