The Unmute Gaza movement, which supports photojournalists reporting from the war zone, also took part in the action.
ADVERTISEMENTHuman rights and environmental activists demanding a ceasefire in Gaza unfurled a giant picture of a Palestinian child crying for help above the entrance to Madrid's Reina Sofia museum on Wednesday.
The banner was illustrated by US street artist Shepard Fairey, also known as 'Obey', and based on an image taken by Gazan photographer Belal Khaled.
It reads: "Can you hear us?" and has an "unmute" sign on the child's face.
Onlookers clapped and cheered when one of the activists unfurled a 'Ceasefire Now; banner.
Police, ambulances and fire service looked on without intervening as the activists made their two-hour ascent of the elevator shaft outside the museum.
The museum houses Picasso's mural-sized work "Guernica", inspired by a 1937 Nazi air raid on a northern Spanish town that killed as many as 1,600 people. The painting is widely considered one of the anti-war masterpieces of 20th century art.