Global leaders met in Istanbul on Monday to tackle a "broken" humanitarian system that has left 130 million people in need of aid, a near insurmountable task for a two-day summit that critics say risks achieving little.

Billed as the first of its kind, the United Nations summit aims to develop a better response to what has called the worst humanitarian crisis since World War Two, mobilise more funds and find agreement on better caring for displaced civilians.

UN Secretary-General Ban Ki-moon called on governments, businesses and aid groups to commit to halving the number of displaced civilians by 2030. "We are here to shape a different future," he said in an address at the start of the conference.

"I urge you to ... find better long-term solutions for refugees and displaced people based on (a) more equal sharing of responsibilities."

Regional wars and failed states

But that may be difficult to attain. The global aid agency Medecins sans Frontieres pulled out of the conference earlier this month saying it had lost hope the participants could address weaknesses in emergency response.

Critics say the global aid system needs greater financing to cope with a proliferation of regional wars and failed states that have ballooned the numbers of displaced people, and to reduce inefficiency and corruption that consume considerable humanitarian funds before they can benefit those most in need.

President Tayyip Erdogan of Turkey, which is saddled with around three million refugees from neighbouring Syria's civil war - the world's largest refugee population in a single country, again accused the West of doing little to help Syrians.

Erdogan has been among President Bashar al-Assad's fiercest critics and sees his removal as essential to ending Syria's war.

"The extent to which the international humanitarian system lies broken is alarming," he wrote in an opinion piece published in Britain's Guardian newspaper. "The international community in particular has largely ignored its responsibilities toward the Syrian people by turning a blind eye to Bashar al-Assad's crimes against his own citizens."

Of political interests

Turkey has run up around $10 billion in costs in taking in the majority of Syrian refugees since 2011, and the West's perceived futility in brokering a halt to Syria's multi-factional conflict has long been a sore point for Erdogan.

Addressing the summit on Monday, he criticised the UN Security Council, saying it should have more than five permanent members - the United States, Britain, France, Russia and China.

"It is illogical, unconscionable and unfair to confine all peoples' fate to the political interest of five countries."

Some 6,000 participants from 150 UN member states were expected at the Istanbul talks, including 57 heads of state or government.

German Chancellor Angela Merkel said there needed to be improvements in how humanitarian aid is delivered.

She was due to meet Erdogan during the summit and has said she would raise the Turkish parliament's vote last week to strip its members of immunity, voicing disquiet at a measure likely meant to sideline the pro-Kurdish opposition.

Merkel is facing accusations at home that she has become too accommodating of Erdogan, who faces accusations of creeping authoritarianism, as she tries to secure a European Union deal with Ankara to stem an influx of refugees from Turkey.

Turkey's pro-Kurdish opposition party said in a statement the summit was being held at a time when democracy and social peace were being undermined by "state violence" in Turkey - an allusion to a major crackdown on Kurdish militants fighting for autonomy in the country's mainly Kurdish southeast.