Mourners flooded the streets of Gaza on Friday as they carried the shrouded bodies of 21 people, including at least eight children, killed in a fire in an apartment block where residents had planned to celebrate the homecoming of a relative.

Most of the dead were members of the Abu Rayya family, their bodies wrapped in Palestinian flags and brought into a mosque for prayers over their souls, before being buried at the Cemetery of Martyrs east of the Jabalia refugee camp.

The Islamist Hamas group, which has ruled the Gaza Strip since 2007, gave the victims a military funeral.

It took firefighters more than an hour to get control of the massive flames that burst through the top floor of a four-story residential building in Jabalia, one of eight refugee camps in the Gaza Strip, where 2.3 million people live in one of the most densely populated areas on earth.

Details about how or why the fire broke remain unclear as there were no survivors, Abu Ahmad Abu Rayya, the head of the clan, said.

“A father, his children and his grandchildren, not one of them got out alive to tell us what happened,” Abu Rayya told the crowds with a strained voice.

Gaza’s Interior Ministry said it had launched an investigation into the incident which revealed that large amounts of gasoline had been stored at the site, possibly fuelling the blaze that quickly engulfed the building.

Palestinian President Mahmoud Abbas called it a national tragedy and declared Friday a day of mourning.

Several Arab states, the United Nations and the European Union expressed their condolences for the bereaved families.

Palestinian officials said a nearly 15-year-long blockade on Gaza has crippled the economy and undermined their effort to upgrade the capability of the enclave’s civil emergency department to fight fires, especially in high rise-buildings.

Citing security concerns with Gaza’s Hamas rulers, both Israel and Egypt maintain restrictions along their frontiers with the coastal territory.