Almost 26 million people have been affected by the deadly earthquake that ravaged Turkey and Syria this week, the WHO said Saturday, warning that dozens of hospitals had been damaged.

As the death toll from the quake rose above 25,000, the UN health agency launched a flash appeal Saturday asking for $42.8 million to help it address the immediate, towering health needs.

The World Health Organization, which has already released $16 million from its emergency fund, had previously said up to 23 million people could be impacted.

But on Saturday, that rose to nearly 26 million, with 15 million affected in Turkey and nearly 11 million in war-torn Syria.

Among them, more than five million people were considered to be particularly vulnerable, including close to 350,000 elderly people and over 1.4 million children.

WHO estimated that in Turkey, where more than 4,000 buildings collapsed in the quake, 15 hospitals had suffered partial or heavy damage.

In Syria, where the health care system had already been ravaged by 12 years of civil war, at least 20 health facilities across the hard-hit northwest, including four hospitals, had sustained damage.

This is making it all the more difficult to help the tens of thousands of people who have been injured in the disaster.

And while emergency medical services have been overwhelmed with trauma patients, essential health services have been severely disrupted, WHO warned.

The UN agency said there was a dire need for immediate trauma care, post-trauma rehabilitative care, essential medicines, prevention and control to prevent disease outbreaks and access to mental health support.

'WHO's goal is to save lives in the immediate aftermath of the disaster, to minimise its downstream health consequences, including mental health, and to rapidly restore essential health services across all earthquake-affected populations.'

The agency added that it had flown 37 metric tonnes of trauma and emergency surgery supplies to Turkey on Thursday, while 35 metric tonnes had arrived in Syria on Friday.

'These life-saving supplies will be used to treat and care for 100,000 people as well as for 120,000 urgent surgical interventions in both countries,' it said.

A third flight carrying a similar load was scheduled to reach Syria on Monday.

WHO chief Tedros Adhanom Ghebreyesus, who arrived in Aleppo on Saturday, tweeted that he was 'heartbroken to see the conditions survivors are facing ... freezing weather and extremely limited access to shelter, food, water, heat and medical care'.