With senior officials from across the world gathered in Kuwait on Tuesday, United Nations Secretary-General Ban Ki-moon said "regional stability is buckling" because of the four-year-old Syria crisis, and "almost 5 million Syrians are still trapped" in besieged areas.

The UN chief and other senior officials were attending the Third International Humanitarian Pledging Conference for Syria, which is hosted by Kuwait.

As many as 78 countries and over 40 international organizations gathered in Kuwait for the third time in three years with high hopes that pledges will exceed those made during the past two conferences, which were held in 2013 and 2014 respectively, according to Kuwait News Agency (KUNA).

Ban warned that "the Syrian people are victims of the worst humanitarian crisis of our time", and "regional stability is buckling under the weight of the Syrian crisis".

According to statistics by conservative estimates, more than 220,000 Syrians are now dead, and the UN chief said "this number is likely much higher".

The world is "about to reach yet another grim milestone" as close to 4 million people have sought refuge status in neighboring countries, Ban said.

"Everyday it gets worse - for the people of Syria and the region at large," Ban added.

The Amir of Kuwait, Sheikh Sabah Al Ahmed Al Jaber Al Sabah, told the conference that he hoped donors attending the event would generously contribute to alleviate the suffering of the Syrian people.

The amir announced a $500 million pledge from the Kuwaiti government and private sectors to support the humanitarian needs of the Syrian people.

Donors, it's hoped, "put this tragedy in front of their own eyes and work to heal the wounds of the Syrian people who have suffered a lot", KUNA quoted him as saying.

Ban said more than 90 percent of last year's pledges of $2.4 billion have been committed, yet as needs continue to grow so do the appeals, which are $8.4 billion.