A flotilla of dozens of boats loaded with aid for Gaza, bearing activists including climate campaigner Greta Thunberg, departed Barcelona on Monday evening for a second time, after stormy weather forced them to return to port earlier in the day.

Some of the boats of the Global Sumud Flotilla Mission blew their horns as they left the port.

“Free, free Palestine,” shouted some activists at the port.

It wasn’t immediately clear how many vessels departed on Monday. Organizers had previously said that there were around 20 boats with participants from 44 countries. Dozens more vessels were expected to join the flotilla from across the Mediterranean later this week.

The flotilla carrying pro-Palestinian and anti-Israel activists had departed Barcelona on Sunday under much fanfare, but was forced back to port on Monday morning after a storm hit parts of Spain overnight.

The Global Sumud Flotilla, consisting of around 20 boats with participants from 44 countries, chose to return and delay its departure to “prioritize safety,” a statement said.

Facing winds of over 56 kilometers per hour (35 miles per hour), some of the smaller boats taking part in the mission would have been at risk, it said.

The flotilla is the largest attempt yet to break the blockade of the coastal Palestinian territory by sea.

Israel and Egypt have imposed varying degrees of blockade on Gaza since Hamas seized power from rival Palestinian forces in 2007 in a violent coup. Israel says it is necessary to limit Hamas’s ability to smuggle in arms. Critics of the blockade say it amounts to collective punishment of Gaza’s roughly 2 million Palestinians.

Activists on board have demanded safe passage to deliver the symbolic aid and the opening of a humanitarian sea corridor, according to a statement.

Thousands of pro-Palestinian supporters had gathered on the docks of Barcelona’s old port Sunday to cheer the mission as it departed for the first time.

It is not the first time Thunberg has attempted to reach Gaza’s waters this year. Israel deported her in June after the Madleen, the ship she was traveling on with 11 other people, was stopped by the Israel Defense Forces.

The flotilla’s departure comes as Israel has stepped up its offensive on Gaza City and prepares to capture the densely populated city in the northern part of the enclave. As part of its preparations, Jerusalem is planning to slow or halt humanitarian aid to the area, an Israeli official told the Associated Press on Saturday.

Food experts warned earlier this month that Gaza City had fallen into famine, and that half a million people across the Strip were facing catastrophic levels of hunger — claims that were swiftly rejected by Israel, which pointed to the thousands of tons of aid that have entered in recent months.

Israel has already blocked two attempts by activists to breach the naval blockade, in June and July. Israel says that the flotillas are propaganda stunts that aid Hamas.

In July, Israeli forces seized the Handala and brought it to port in Ashdod. Activists from 10 countries, including two French MPs from the left-wing France Unbowed party, were detained, then deported.

In June, 12 activists on board the Madleen, from France, Germany, Brazil, Turkey, Sweden, Spain and the Netherlands, were intercepted by Israeli forces 185 kilometers (115 miles) west of Gaza. They were detained and eventually expelled.

The war in Gaza was triggered by an unprecedented cross-border attack by the Hamas terrorist organization into Israel on October 7, 2023, in which some 1,200 people were killed and 251 taken hostage.

The Hamas-run Gaza health ministry says more than 62,000 people in the Strip have been killed or are presumed dead in the fighting so far, though the toll cannot be verified and does not differentiate between civilians and fighters.

Israel says it killed over 22,000 combatants in battle as of August and another 1,600 terrorists inside Israel during the October 7 onslaught. Israel has said it seeks to minimize civilian fatalities and stresses that Hamas uses Gaza’s civilians as human shields, fighting from civilian areas including homes, hospitals, schools, and mosques.