Vienna underground/Kurdish rally
Local media said four teenagers were screaming chant, which translates as “God is greatest” in Arabic, while waving and firing replica weapons.
Witness Amer Albayati, an Austrian-Iraqi journalist and terrorism expert, said passengers panicked and tried to get away from teenagers during the incident near the Schweglerstrasse station.
One passenger tried to overpower the migrant mob and managed bundle them off the train.
Police spokesman Thomas Keiblinger said the incident was under investigation and that officers were searching for four youngsters aged between 10 and 16-years-old.
Kurdish protestors scatter as a man shouts Allahu Akbar
Vienna public transport services spokesman Daniel Amann said: "We have safety precautions on the train and on the platforms for precisely those incidents where passengers are not feeling secure."
The underground incident comes just days after a protest rally ended in chaos when a man ran into the crowd shouting "Allahu Akbar", sparking fears of an imminent terror attack.
It happened during a regular demonstration by Kurdish nationals and their supporters in Austrian capital Vienna.
Kurdish campaigners gather in the city’s famous Stehpansplatz every Saturday to draw attention to alleged human rights abuses against their people in Turkey.
But last weekend the situation escalated when the demonstrators were attacked by a group of Turks, one of whom cried out "Allahu Akbar", causing mass panic.
Chaos erupts during a pro-Kurdish rally in Austrian capital Vienna
Some senior citizens were sitting on our stairs and crying
Aida chef Sonja Prousek
Video footage of the ensuing pandemonium shows people fleeing the square and scattering in different directions after the shouts were heard.
Terrified children were separated from their parents and some people were pushed to the ground in the stampede as they tried to run away.
Riot police in full protective gear intervened quickly to stamp out any disorder and restore calm to the historic square.
But the outdoor seating area of traditional Viennese coffee shop Aida was destroyed in the melee.
Aida chef Sonja Prousek described the scenes as "straight from a war zone".
She said: "Tables and dishes flew into the air. Food lay on the ground. Our outdoor cafe was completely ravaged and we had to close our branch. Some senior citizens were sitting on our stairs and crying."
A cafe forecourt is trashed as people flee the area
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Businesses in the city centre of Vienna are becoming increasingly concerned by the weekly protests.
Ms Prousek said: "Whenever there is a demonstration we have an empty establishment. The people are afraid.
"Police are not happy with the scenes either but they said the people had the freedom to organise the protest."
Police in Vienna had to intervene at the national public broadcaster ORF last Friday night when Kurdish protestors tried to storm the building to call for the reading of a press release during the Austrian evening news.