The World Health Organisation has said the earthquake that hit Turkey and Syria has "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.