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

It marks one of the deadliest incidents in recent years outside the violence stemming from the Israeli-Palestinian conflict.

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 the densely-populated Jabalia refugee camp in the northern Gaza Strip.

Ambulances rushed several injured people to local hospitals, and Israel, which together with Egypt maintains a blockade on Gaza, said it would allow in those in need of medical treatment.

The head of the Indonesian Hospital in Jabalia, Saleh abu Laila, told Agence France-Presse (AFP) that the facility had received the bodies of at least seven children killed.

Gaza's Interior Ministry said an initial investigation revealed that large amounts of gasoline had been stored at the site, fueling the blaze that quickly engulfed the building.

Witnesses said they could hear screaming but they could not help those inside because of the intensity of the fire.

Gaza faces a severe energy crisis. People often store cooking gas, diesel and gasoline in homes in preparation for winter. House fires have previously been caused by candles and gas leaks.

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

Türkiye extended condolences to the families of those killed and the Palestinian people and wished a speedy recovery to those injured, a statement by the Foreign Ministry said.

Hussein Al-Sheikh, a senior Palestinian Authority official, called on Israel to open its border crossing with Gaza to allow for the evacuation of those injured who need advanced medical care to Palestinian hospitals in the West Bank and Jerusalem.

"The President gave instructions to provide all forms of medical and other assistance urgently," Al-Sheikh said on Twitter.

Tor Wennesland, the United Nations' Middle East peace envoy expressed "heartfelt condolences" to the families of those who died in the incident, in a post on Twitter.

Jabalia is one of eight refugee camps in Gaza, home to 2.3 million people and one of the world's most densely populated areas.