Spanish unions are holding a general strike to protest against labour reforms which the new government hopes will help cut unemployment.
Road, rail and air transport are all due to be affected, with domestic and European flights cut to a fraction of their usual volume.
Mariano Rajoy's conservative government is to unveil measures on Friday to save tens of billions of euros.
The strike is the government's first big challenge since taking office.
Scuffles broke out between protesters and police as workers from Spain's largest unions picketed at the capital's bus depot early on Thursday.
The interior ministry said a total of 58 people were detained and nine were injured.
Outside Atocha - one of Madrid's main rail stations - picketers waved red union flags and blew shrill whistles as police looked on.
Overnight, the UGT union said that participation in the strike was "massive" and said that virtually all workers at Renault, SEAT, Volkswagen and Ford car factories around Spain had honoured it during the shift.
Regional TV stations in Andalusia in the south, Catalonia in the northeast and Madrid were also off-air because of the strike.
With the EU's highest rate of unemployment, Spain is under pressure to reduce its budget deficit and bring its public finances under control.
"The question here is not whether the strike is honoured by many or few, but rather whether we get out of the crisis," the country's Finance Minister Cristobal Montoro said.
"That is what is at stake, and the government is not going to yield."
The country's two biggest unions called the strike to demonstrate against new legislation which makes it easier and cheaper for companies to fire employees.
Protest marches are planned throughout the country during the evening.
The new legislation, approved in February, also reduces maximum severance pay to 33 days' salary for each year worked, compared with the current 45 days.
The government insists the reforms will create a more flexible system for businesses and workers, in a country with a stagnant economy that needs to start creating jobs.
Polls have suggested only 30% of workers will take part in the strike but observers say the results of regional elections on Sunday - which punished the ruling People's Party - may lead to greater participation.
Ignacio Fernandez Toxo, leader of the CCOO trade union, said the strike was "a just response to a brutal reform of our system of labour relations".
One protester in the capital Madrid, Maria Jose, said: "This labour reform was meant to protect entrepreneurs and what it really protects are big companies.
"That is why we are here fighting together."
Under an agreement between the government and the 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.
Mr Rajoy, who took office in December, defended his measures on the grounds that they would eventually generate more jobs.
"No government has passed as many reforms in its first 100 days in office as this one," he said on Tuesday, speaking on a visit to South Korea.
"The biggest mistake would be to do nothing," the Spanish prime minister added.