The WHO said the health needs in the Gaza Strip were soaring while its ability to address them was plunging.

The UN health agency has been able to deliver 54 metric tonnes of humanitarian supplies into the territory over the past fortnight but said that would not even begin to address the scale of need.

"WHO will do everything we can to ensure that all people in Gaza have access to life-saving health and humanitarian services," WHO chief Tedros Adhanom Ghebreyesus told a press conference.

"In the current situation, this is almost impossible."

The WHO's emergencies director Michael Ryan said the basic safety of staff on the ground in Gaza could not be guaranteed at the moment -- something he branded "unconscionable".

He said the organisation had never found it as difficult to establish basic rules of engagement regarding minimum safety guarantees for humanitarians.

"It is the responsibility of all parties to the conflict to allow those hospitals to be resupplied," Ryan said.

"Occupying authorities have a special responsibility to ensure that such facilities are not only protected but serviced and supplied with the adequate needs for the populations that they serve.

"Right now, we have no deconfliction effectively operating. There is no humanitarian access.

"It has been almost impossible to set up appropriate notification acknowledgment and deconfliction measures."

Getting medical supplies to where they are needed "has not been facilitated, that has not been supported; in fact, if anything, quite the opposite".