The World Health Organisation has said the earthquake that hit Turkey and Syria have “overwhelmed everyone” – amid warnings the flow of aid must be urgently sped up to save lives.

The number of people killed in both countries continues to grow and now stands at more than 33,000.

Dr Michael Ryan, WHO’s executive director, said it was “misleading” to compare the impact in both countries, with so much relying on the “extent of the earthquake” and “population density”.

“There’s no question, certainly on the side of Turkey, there’s a matter of experience in terms of search and rescue, in terms of disaster response,” said Dr Ryan.

“They have had their fair share of disasters in the past – but I think what’s clear is that this disaster has overwhelmed everyone.”

There has been criticism of the amount of aid reaching Syria – the worst-affected area is largely controlled by an Islamist group that is wary of shipments from government-held areas.

There is also only one border crossing open from Turkey to northwest Syria and the first UN convoy only reached the area on Thursday.

The WHO panel, speaking in Syria, said the country was not only battling the aftermath but also freezing temperatures and the end of a cholera outbreak.

Regional emergency director Dr Rick Brennan said around 350,000 people in Aleppo and Latakia were left homeless instantly and that providing care was an “enormous undertaking”.

He said many were being housed in mosques, schools, churches and centres, but that overcrowding is a problem.

“They are not acceptable conditions, so we are working with partners to look at other options,” he said.

There is also an increased risk of catching a disease due to the huge number of people and poor sanitation.

Syrian people ‘abandoned’

The UN’s emergency relief co-ordinator, Martin Griffiths, is heading to Syria to try to urgently improve the flow of aid.

“We have so far failed the people in northwest Syria. They rightly feel abandoned. Looking for international help that hasn’t arrived,” he tweeted on Sunday.

He told Sky’s Kay Burley that extra border crossings from Turkey to Syria must be opened urgently “to save lives”, calling it an “an open and shut case on humanitarian terms”.

Andrew Mitchell, the UK development minister, also admitted in a Sky News interview that aid Syria was “far more stretched” than in its neighbour.

He said he believed total deaths across both countries could end up being around 50,000.

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Meanwhile, the amount raised by people in Britain passed £60m in just three days, the Disasters Emergency Committee said on Sunday.

The committee distributes the money among a group of leading UK aid charities.

A week on from Monday’s earthquake, the chances of more people being dug out alive – like the boy rescued after five days – is all but gone.

The focus is now on recovering the countless bodies trapped under rubble of the countless buildings that collapsed.

Some 131 people involving in the building industry have been detained or had warrants issued for their arrest, according to Turkish vice president Fuat Oktay.

Many of the buildings that crumbled are believed to have not been robust enough, as construction codes are rarely enforced in the country.

The justice ministry has said it will set up an Earthquake Crimes Investigation bureau.

Looting of businesses and homes has also been reported in some areas of Turkey, with the country’s justice minister saying on Sunday that 57 people had been arrested.

President Erdogan has said thieves will be dealt with firmly, but some business owners have been seen emptying their shops.

Two German aid organisations and rescuers from the Austrian army were also forced to pause work for a time on Saturday, citing “clashes between different groups” and “shots fired” in one Turkish town.