The World Health Organization (WHO) Thursday slammed the lack of safety guarantees for bringing humanitarian aid into the Gaza Strip, saying it was near impossible to get medical supplies to hospitals.

The WHO said the health needs 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 organization had never found it as difficult to establish basic rules of engagement regarding minimum safety guarantees for humanitarians.