Workers endured stormy weather to set up picket lines on Wednesday, with large marches taking place in Madrid, Barcelona and cities across Spain less than three weeks before a snap general election.
In the evening, clashes between police and some protesters erupted in Barcelona. Reuters footage showed furniture on the street had been set on fire after the main march had ended.
Tensions also rose in Madrid, when riot police used foam bullets, tear gas and pepper spray to disperse protesters around the central Plaza de España, a Reuters witness said.
Police forces reported at least 73 arrests nationwide from at least 1044 incidents linked to the general strike, including blockades of offices and industrial estates and burning of rubbish containers.
It is the first general strike since workers downed tools in 2012 against austerity measures during the euro zone debt crisis. The walkout is backed by Spain's two largest unions, the General Union of Workers (UGT) and the Workers' Commissions (CCOO), representing more than one million workers, as well as tenants' associations angry about rising rents and evictions.
Prime Minister Pedro Sanchez hopes to harness voter resentment over housing in the November 29 election to shift the attention away from a deadly migration incident in Ceuta and a train crash in October. His government has defended its handling of the disasters but so far, his Socialist Party still trails in opinion polls.
Unions described the strike as a success even though participation was uneven across Spain, with the strongest support in coastal regions where housing pressures have been particularly acute.
Spain has a deficit of about 750,000 homes, which is set to grow to more than one million by 2028, according to the central bank.
With fewer people able to afford a home, renting has increased sharply, putting pressure on that market. The average rental price of €1176 ($A1920) is equivalent to about 98.7 per cent of a young person's average monthly salary in Spain, according to the Youth Council of Spain.
Two heavy storms, dubbed Charles and Bruna, threatened plans for massive protest marches in the afternoon, with unions suspending demonstrations in the southern port city of Cadiz and other cities in the south.
The tenants' union said it still expected participation in the strike to reach five million people by the end of the day. Spain has around 23 million workers, according to the national statistics institute.
The strike follows weeks of demonstrations provoked by the eviction and subsequent death of an 87-year-old woman in Madrid.
Those protests, along with parliament's rejection of government decrees aimed at curbing evictions and limiting rent pressures, prompted Sanchez to call the snap election.
