Transport and public sector services affected as workers strike against austerity measures and labour reform.
A 24-hour general strike is taking place in Spain, grounding flights and disrupting public sector services.
Thursday's strike was called by trade unions protesting against labour reforms and spending cuts which the conservative government says are needed to save the economy.
"This is a just response to a brutal reform of our system of labour relations," Ignacio Fernandez Toxo, leader of the CCOO, one of the main trade unions, said.
The strike is the first major walkout against the government's policies, just three months after Mariano Rajoy, the prime minister, took office promising to cut Spain's 23-per cent unemployment rate and stabilise its public finances.
Scuffles broke out between protesters and police as workers picketed the capital's bus depot early on Thursday.
Around 100 protesters gathered in front of Fuencarral's bus depot and some of them blocked the road as the first bus departed form the depot. Tensions rose as riot police wrestled some protesters to the ground.
Street demonstrations have also been called, mostly for the evening when many people will have finished work.
Thousands of demonstrators gathered in Madrid's Puerta del Sol square on Wednesday.
A recent poll showed that three quarters of Spaniards are against labour reform, but a majority also believe that a general strike may make the situation worse. Only 30 per cent of workers would join the walkout, according to polls.
'Very austere budget'
Under an agreement between the government and the two main unions, at least a minimum service of a third of local trains and buses is due to run, with one in 10 domestic and one in five European flights.
Airlines Iberia, Air Nostrum and Vueling have cancelled about 200 flights each from Spanish airports.
A minimum service is also planned in hospitals while schools and nurseries are due to open.
The national strike comes a day before the government unveils its 2012 budget, raising the heat on Rajoy who also faces pressure from European leaders to cut Spain's public deficit and avert further financial instability in the eurozone.
Rajoy, who has promised a "very austere budget", has defended his measures, including labour reforms which make it easier for firms to hire and fire and reduced severance pay for laid-off workers.
He says the proposed legislation would eventually generate more jobs.
"No government has passed as many reforms in its first 100 days in office as this one," Rajoy said.
"That's probably why there is a general strike," but it "will not solve Spain's problems, the biggest mistake would be to do nothing," he added.
Rajoy has so far this year confirmed $11.85bn worth of spending cuts and $8.39bn in tax rises, but economists say total cuts worth more than $66.6bn are needed.