Healthcare systems of neighbouring countries are feeling the strain as thousands of critical patients from the Gaza Strip are evacuated for treatment of complex injuries and ailments, a top WHO official said on Tuesday.

"The ripple effect on Egypt, Lebanon, Syria as the immediate neighbours of the OPT (occupied Palestinian territories) is significant," said Hanan Balkhy, the World Health Organization's regional director for the Eastern Mediterranean.

Fewer than half of Gaza's 36 hospitals are partially functional as of May 30, the global body has reported, as most of the medical infrastructure has been destroyed by Israel's eight-month-old assault.

"Egypt has been hosting a significant number of the patients, but the needs are between minimum 7,000 to over 11,000 patients that require evacuation and treatment and support," she said at a briefing with journalists. "And they require it in specialized hospitals."

This has caused pressure on "already fragile health systems in the neighbouring countries."

"It's not like sewing a laceration," she added, referring to the typical injuries seen among patients from Gaza.

"You're talking about compound fractures, skull fractures, compound femur fractures, ruptured visceral organs... It's very difficult to find and to quickly transport patients to get that type of care."

No medical evacuations have been carried out since May 7, after Israel took control of the Rafah crossing, according to WHO.

The closure of the crossing in the south of the Gaza Strip has also significantly affected the WHO's ability to deliver essential medical supplies to the enclave.

(Reporting by Gabrielle Tétrault-Farber; Editing by Sriraj Kalluvila)