United Nations Secretary-General Antonio Guterres issued a strong condemnation of the hospital blast in Gaza that killed hundreds of Palestinians.

"I am horrified by the killing of hundreds of Palestinian civilians in a strike on a hospital in Gaza today, which I strongly condemn," he wrote on X, formerly known as Twitter.

"My heart is with the families of the victims. Hospitals and medical personnel are protected under international humanitarian law," he said.

Outrage has been growing over the hospital blast. The UN Security Council will hold an emergency meeting on the matter on Wednesday morning following calls from the UAE and Russia.

EU foreign policy chief Josep Borrell and French President Emmanuel Macron joined the condemnation, although like with Guterres, neither said who they believed to be responsible for the strike.

"The news coming from the Al-Ahli Arabi Baptist hospital in Gaza add horror to the tragedy unfolding before our eyes since days," Borrell said.

"Once again, innocent civilians pay the highest price. The responsibility for this crime must be clearly established & the perpetrators held accountable," he added.

"Nothing can justify striking a hospital. Nothing can justify targeting civilians. France condemns the attack on the Al-Ahli Arab hospital in Gaza, which made so many Palestinian victims,"  President Macron wrote on social media.

"Humanitarian access to the Gaza Strip must be opened back without delay."

US President Joe Biden also expressed his "outrage" over the incident while flying to Tel Aviv where he is expected to stress his support for Israel.

"I am outraged and deeply saddened by the explosion at the Al-Ahli Arab hospital in Gaza, and the terrible loss of life that resulted," he said.

Biden said he had directed his national security team to look into what happened.