Thousands of people were left trapped on trains or stranded overnight after the theft of copper cables halted high-speed services between Madrid and southern Spain's Andalusia region.

Authorities opened an investigation on Monday after Sunday's theft, which Transport Minister Óscar Puente called a "serious act of sabotage".

He added that the cable theft took place at five locations, all within a few kilometres of each other on the high-speed line. On Monday morning, Puente said train operations were being "fully restored" .

This travel disruption comes a week after Spain and Portugal suffered a blackout, which similarly saw trains come to a standstill. The cause is still unknown.

"All of a sudden, in the last two weeks - what is going on?" Kevin, a tourist from the US, told Reuters news agency as he waited at Madrid's Atocha station, where thousands were stranded.

More than 10,000 passengers were affected between Madrid, Seville, Malaga, Valencia and Granada, and at least 30 trains.

The disruption came after a long weekend in Madrid and ahead of the week-long Feria festival in Seville, which sees an influx of travellers to the city.

"Operations are now fully restored after a very difficult night for commuters... and staff, who had to respond under extremely complex circumstances," the transport minister said on Monday morning.

The theft locations, he said, were in areas accessed via forest trails.

Train services were gradually returning to normal, Spain's national rail manager Adif said on Monday afternoon.

Earlier in the day, the Spanish interior ministry said the country's civil guard and police were in contact with Adif and other authorities to "clarify what happened and identify those responsible".

The price of copper has soared in recent years, and cable thefts from trains and telecommunications networks have surged.