France's largest nationwide strike in years has severely disrupted schools and transport. Workers are angry about planned pension reforms that would see them retiring later or facing reduced payouts. School and transport workers have been joined by police, lawyers and hospital and airport staff for a general walkout that could include millions of people. President Emmanuel Macron wants to introduce a universal points-based pension system. That would replace France's current system, which has 42 different pension schemes for its private and public sectors, with variations in retirement age and benefits. "What we've got to do is shut the economy down," said union official Christian Grolier of the Force Ouvrière (Workers' Force). "People are spoiling for a fight." Interior Minister Christophe Castaner said on the eve of the strike that he expected almost 250 demonstrations nationwide, some of which he said could turn violent. On Paris's famous Champs-Élysées boulevard, riot police began searching pedestrians' bags before dawn. Popular tourist sites including the Eiffel Tower, the Musée d'Orsay and the Palace of Versailles have shut for the day. As of midday, police in the capital said they had detained 18 people ahead of a planned march towards the Place de la Nation which was set to start at 14:00 local time (13:00 GMT). Shops on the protest route were ordered to close. And in the city of Nantes, protesters were tear-gassed after some threw projectiles at police, French news channel BFM reported.