At least 21 people have been killed and several others injured when a fire broke out in a building where residents attended a party in the Gaza Strip, health and civil emergency officials said on Thursday.

It reportedly took Firefighters over an hour to bring the flames that burst through the top floor of a four-story residential building in the densely-populated Jabalia refugee camp in northern Gaza Strip under control.

The UN agency for Palestinian refugees (UNRWA) tweeted that reports say among those killed include eight children, four women and one retired UNRWA staff.

According to Reuters, Gaza’s Interior Ministry said an initial investigation revealed that large amounts of gasoline had been stored at the site, fuelling the blaze that quickly engulfed the building.

Palestinian President Mahmoud Abbas called it a national tragedy and said there would be a day of mourning.

Hussein Al-Sheikh, secretary-general of the executive committee of the Palestine Liberation Organization (PLO), said in a statement that the Palestinian Authority urged Israel to open the Erez crossing with Gaza to transport serious cases in order to treat them outside the enclave if necessary.

Sheikh said on Twitter: “The President gave instructions to provide all forms of medical and other assistance urgently.”