Thousands of people protested on Saturday in Germany, France, Switzerland, Albania and Portugal. Some cities saw clashes and petrol bombs, and hundreds of people were arrested, police and officials in each country said.
Protesters cited the rising cost of living, police violence, conditions in education, social justice and climate protection.
France had the most arrests, with protests in about 30 cities. An interior ministry report issued at 9pm local time said 565 people were detained nationwide. Clashes broke out in Paris, Lyon, Bordeaux, Marseille, Lille and Toulouse. Police used tear gas, pepper spray and water cannon.
It was the third big day of protest in France in three weeks, after 17 and 24 October. Turnout figures differ. The interior ministry said about 320,000 people took part, 70,000 of them in Paris. The International Youth Union and the youth inter-union organisation put the number at nearly half a million, about 200,000 of them in Paris.
Interior minister Laurent Nuñez condemned the actions of several hundred rioters and called it "incredible violence". He said he regretted that violence against police officers and gendarmes is growing.
At Porte de Charenton in Paris, a petrol bomb hit a police officer and set his clothes on fire. He said he did not see the device land on him. Only when he watched footage of the flames around him did he realise he had narrowly escaped worse injuries. He said a very hostile group gradually gathered and attacked the police position suddenly and brutally.
In Germany, young people protested in 34 cities at the call of the group "Generation Z Decides". The protests were mostly peaceful, but overnight there was looting in a number of big cities, and petrol bombs were thrown at police. German police said today that more than 200 people were detained in all.
In Frankfurt, protesters stormed shops and stole. Police detained about 30 people and seized two weapons, a police spokesperson said.
In Cologne, a group attacked police with bottles and bicycles on the square in front of the cathedral, next to the main railway station. One person was hurt and five were detained. Police chief Johannes Hermanns said officers seized petrol bombs and emergency hammers from masked participants.
In Berlin, people threw firecrackers, fireworks and eggs at police and journalists. Pro-Palestinian supporters with Palestinian flags also joined the protest. A Berlin police spokesperson said 56 people were detained and almost 30 officers were hurt.
In Hamburg, about 6,700 people took part, police said. Dressed in black, some in masks, they set barriers on fire. Police dispersed the crowd with pepper spray and put out the fire with a water cannon. About 120 people were detained.
In Switzerland, protesters and police clashed in Zurich and Basel, where barricades were set on fire and property was damaged. In Zurich, clashes between left-wing demonstrators and police began around 11pm local time near Langstrasse and Helvetiaplatz. Police used water cannon, tear gas and rubber bullets. The situation calmed around 1:30am, but extra police remain on the streets.
Zurich city police said many of those taking part wore Halloween costumes, and described the group as prone to violence. Protesters surrounded officers and stopped them reaching a road crash in which a minor suffered serious leg injuries.
In Tirana, protesters gathered again and marched towards the office of prime minister Edi Rama, just minutes after police had dispersed them. They chanted "Rama, resign". Police formed a cordon and kept them away from the government building. They used pepper spray when protesters refused to walk on the pavement and tried to pass in front of the building.
Several people were detained after clashes outside the education ministry, where petrol bombs were thrown. Police units are patrolling several parts of the city to find and detain suspects over the incidents.
In Porto, thousands of people joined a march for more affordable housing. The column left Batalha square at about 4:50pm local time and reached Dom João I square about 50 minutes later. A green banner reading "A home for life" led the way, and marchers also carried a tent.
They chanted "Resistance, resistance" and "Roof, land, right to housing" and urged passers-by to join. They sent a message to the interior minister that the right to housing is a basic democratic right.