The 'Global Sumud Flotilla' says it has assembled the largest civilian flotilla in history aiming to get beyond the Israeli blockade and bring humanitarian aid to Gaza.

Organizers, activists, doctors and crew set sail from the Spanish port of Barcelona on Sunday to try to "break the illegal siege of Gaza."

It's the first convoy to take to the seas, made up of dozens of small civilian vessels and will join up with the rest of the fleet in Tunisia on September 4, more than 50 ships in all are expected to make the journey.

This broad alliance of civilian and humanitarian organisations says the goal is to "open a humanitarian corridor and end the ongoing genocide of the Palestinian people."

Brazilian activist Thiago Avila called it "the largest solidarity mission in history." He sat next to Swedish activist Greta Thunberg at the press conference in Barcelona pre-boarding.

"The question here today is not why we are sailing," Thunberg stated, "the story is not at all about the mission we are about to embark. The story here is about Palestine, the story here is how people are being deliberately deprived of the very basic means to survive."

Game of Thrones actor in tears over Palestinian death

Irish 'Game of Thrones' actor Liam Cunningham fought back tears at the same press conference while playing a recording on his phone of a Palestinian child named Fatima singing a song she wanted someone to sing at her funeral, just days before she was killed by Israeli forces.

"What sort of world have we slid into? What sort of a human hole have we found ourselves in? When children, beautiful angels like that, of five or six years old and making their own funeral arrangements?" Cunningham said.

He added: "And the fact that you guys are here and the flotilla is happening is an indication of the world's failure to uphold international law and humanitarian law and is a shameful, shameful period in the history of our world."

Conscience - drone strike survivor

'Conscience' was one of the vessels present in Barcelona, a powerful symbol of resilience and defiance for the activists after it made global headlines in Spring when it was attacked by a drone off the coast of Malta on May 2 - the damage from the strike still visible on Sunday.

Two 'Freedom Flotilla' vessels have already been detained by Israeli forces before reaching Gaza.

In June the sailing vessel the Madleen was intercepted by Israeli forces 185km west of Gaza with 12 activists on board including Thunberg. They were deported from Israel.

A month later another vessel, the 'Handala,' and 21 activists on board from 10 countries were intercepted.

Now the biggest flotilla yet has set sail to try again.

Asked what they will do if they are stopped again, Yasemin Acar, part of the flotilla's steering committee said "the question should be why would they stop a purely humanitarian mission?"

"We carry no weapons. We are no threat. We are carrying humanitarian aid to a starving population. What we should also ask is why are the governments around the world are not acting? Why are they not sanctioning Israel and lifting the siege so that the humanitarian aid can enter Gaza?"

Thousands gathered in Barcelona in support, and simultaneous pro-Palestinian protests and demonstrations are planned across 44 countries during the mission.

Meanwhile Gazans mourn the death of loved ones from the latest attacks as Israeli ground and air strikes on the strip intensify and victims succumb to a manmade famine.