Thousands of Palestinians have overrun an aid distribution site in Gaza set up by a controversial US and Israeli-backed group, a day after it began working there.

Videos showed crowds walking over torn-down fences and earth berms at the Gaza Humanitarian Foundation's (GHF) compound in the southern city of Rafah.

The group said that at one point its team fell back because the numbers seeking aid were so great. The Israeli military said troops nearby fired warning shots.

The GHF, which uses armed American security contractors, aims to bypass the UN as the main supplier of aid in Gaza, where experts have warned of a looming famine after an 11-week Israeli blockade that was recently eased.

The UN said the videos from Rafah were "heartbreaking" and that it had a detailed plan ready to get enough aid to the "desperate population" of 2.1 million.

The UN and many aid groups have refused to co-operate with GHF's plans, which they say contradict humanitarian principles and appear to "weaponise aid".

They have warned that the system will practically exclude those with mobility issues, force further displacement, expose thousands of people to harm, make aid conditional on political and military aims, and set an unacceptable precedent for aid delivery around the world.

Israel has said an alternative to the current aid system is needed to stop Hamas stealing aid, which the group denies doing.