Power was restored to Spain and Portugal Tuesday after a mysterious blackout hit both countries. 

The blackout caused multiple planes to be grounded, stopped trains and disrupted communications on Monday, according to The Associated Press.

The Spanish electrical system was functioning normally by 11 a.m. Tuesday. The cause of the blackout has still not been determined. 

Portugal’s National Cybersecurity Center said there weren't any signs that the outage came from a cyberattack.

Emergency workers in Spain rescued thousands of passengers stranded along railways.