The Palestinian envoy to Japan has strongly condemned Israel, calling an explosion at a hospital in the Gaza Strip "a stark and harrowing illustration of the grave atrocities committed against unarmed civilians".

Waleed Siam, the Ambassador, Representative of the Permanent General Mission of Palestine, held a news conference in Tokyo on Wednesday.

He accused Israel of targeting a hospital that had many people inside as part of its assault against the Palestinian Islamist group, Hamas. He said it "undeniably constitutes war crimes and is a flagrant violation of fundamental human rights and international law".

He said at least 500 people have been confirmed dead following the airstrike on the hospital on Tuesday and that the tally will likely increase as a large number of bodies have yet to be recovered.

Siam added "it is the responsibility of the international community to stop shielding Israel and stop these war crimes".

His appeal is apparently aimed at US President Joe Biden, who is visiting Israel, among other heads of state.

Siam said Gaza is short of food, medicine and fuel to keep hospitals functioning. He said the medical system there is strained, and that there is an urgent need to open a humanitarian corridor for injured people to be transported to hospitals outside Gaza.

Meanwhile, an event was held outside the Israeli Embassy in Tokyo to mourn the victims killed in attacks by Hamas. Some 100 people, including Israelis living in Japan and the Israeli and US ambassadors to Japan, attended.

An Israeli man in his 50s said the attacks deeply shocked all Israelis including himself.

He expressed his dislike for civilian casualties and war, but he said he wants the world to recognize Israel's right to defend itself as his country came under sudden attack.

Israeli Ambassador to Japan Gilad Cohen said he was moved by the support from so many people. He emphasized that Israel does not target civilians, and asked people in Japan to support Israel.