Madrid, Nov. 12: Police fired tear gas as sporadic clashes broke out in Madrid and Barcelona on Wednesday after huge protests across Spain over housing affordability and purchasing power just weeks before an early general election.

Hundreds of thousands of protesters turned out during Spain's first nationwide 24-hour strike since 2012, with authorities estimating around 120,000 demonstrators marched through the capital and more than 50,000 rallied in Barcelona.

Clashes broke out after the protests in Spain's two largest cities, as groups of hooded and masked demonstrators hurled projectiles at police and sparked fires, according to AFP journalists.

Video footage showed large rubbish skips as well as bicycles and pot plants engulfed in flames on roads in Barcelona with heavy contingents of police vans racing through the streets.

Police used rubber bullet launchers and tear gas to disperse small groups of protesters and arrested 18 people in Barcelona.

The size of the demonstrations has been seen as an indicator of public discontent before a snap election set for this month, in which the right-wing opposition is expected to defeat Socialist Prime Minister Pedro Sanchez.

Braving pouring rain, protesters in Madrid carried placards shaped like houses and chanted "we have no home" as they called for more affordable housing.

"People work a lot and it isn't enough to pay the rent, to pay for a house," Paula Diaz, a 25-year-old theatre technician who lives with her parents, told AFP at the Madrid protest.

"I hope a government that benefits us comes to power, especially the working class," she added, referring to the November 29 election.

In Barcelona, where authorities estimated 55,000 people marched through the city's luxury Passeig de Gracia commercial thoroughfare, Maria Pinana told AFP "the law of supply and demand does not apply to housing".

"The price of rents should be regulated," said the 34-year-old microbiologist, who lives with friends in a flat where parts of the ceiling have collapsed.

Tens of thousands more attended rallies held in other cities across Spain, the latest in a wave of protests sparked by the eviction of an 87-year-old Madrid pensioner in September.-Agencies