At least 500 people are feared to have been killed in a huge explosion at a Christian hospital in Gaza that both Israel and Hamas have denied responsibility for. 

Authorities in Gaza have blamed Tuesday night's explosion at the Al Ahli Arab Hospital in Gaza City on an Israeli air strike.

Israel has denied the involvement of its military and said it was caused by a misfired rocket from the Palestinian Islamic Jihad militant group, the BBC reports. This group has also denied responsibility. 

The Al Ahli Arab Hospital is run by the Episcopal Diocese of Jerusalem. In a statement, the diocese said that an attack on a hospital would be "atrocious" and a "crime against humanity", and that the "targeting of the church" would be "sacrilegious". 

Earlier this week, the Archbishop of Canterbury Justin Welby expressed his concerns about the safety of the hospital and other healthcare facilities in Gaza, and said that the hospital had already been hit by Israeli rocket fire on Saturday night.

Following an evacuation order for northern Gaza, Archbishop Welby said that the Al Ahli Hospital "cannot be safely evacuated". He had urged Israel to overturn the order, saying that hospitals in Gaza were "facing catastrophe". 

The Episcopal Diocese of Jerusalem in its statement echoed the call of Welby for hospitals to be protected and the evacuation order to be reversed. 

"Hospitals, by the tenets of international humanitarian law, are sanctuaries ... Regrettably Gaza remains bereft of safe havens," it said.

It added, "As we grieve the loss of countless souls who perished on our premises, we declare a day of mourning in all our churches and institutions." 

The media office of the Hamas government said that the hospital was sheltering "hundreds of sick and wounded, and people forcibly displaced from their homes".

Palestinian President Mahmoud Abbas has declared three days of mourning "for the martyrs of the Baptist hospital massacre and all our people's martyrs", the official Palestinian news agency Wafa said.

Embrace the Middle East, a partner of the Al Ahli Hospital, said it was "devastated" by reports of a direct hit on the facility, which happened on the same day as churches in the Holy Land and around the world were praying and fasting for peace.

Al Ahli Arab Hospital is the oldest hospital and the only Christian hospital in Gaza. It was founded by the Anglican Church Mission Society in 1882 and then became a Baptist medical mission in 1954. It has been Anglican-run since 1982.

The Archbishop of Dublin, Michael Jackson, called news of the blast "distressing".

"Our friends in the Diocese of Jerusalem have asked for our prayers and our voices at this time. I urge you now to pray for all the people of Gaza and of Israel," he said.

"We pray for peace and that the human dignity and life of every single person in the Land of the Holy One be respected.

"I also urge all people who have a voice in the political arena to raise it now on behalf of all who are living in terror, grief, trauma and facing death."

US President Joe Biden, who is visiting Israel in a show of solidarity, said, "The United States stands unequivocally for the protection of civilian life during conflict and we mourn the patients, medical staff and other innocents killed or wounded in this tragedy."