BEIJING - Twenty-six countries have been so far involved in the difficult search for missing Malaysia Airlines flight MH370, which mysteriously disappeared on March 8 en route from Kuala Lumpur to Beijing.

Experts say the unprecedented, multinational search efforts reflect a laudable spirit of cooperation in the international community, in which China has made notable efforts to find the ill-fated plane with 239 people onboard, including 154 Chinese.

CLOSE INTERNATIONAL COOPERATION

By April 28, the search had covered more than 4.5 million square kilometers of the Southern Indian Ocean.

Australian Prime Minister Tony Abbott said countries involved in the search had shown a remarkable spirit of cooperation.

"This multi-country search is a powerful example of international cooperation at a time of adversity," he said, calling it "a very important humanitarian exercise."

Malaysian Prime Minister Najib Razak said the joint efforts of the 26 countries had brought comfort to the families of passengers on the missing plane, and their contribution would be remembered.

"In a time of great tragedy...differences have been set aside, as 26 nations have united behind a common cause. The disappearance of MH370 is without precedent, so too is the search," the prime minister said.

Ekaterina Koldunova, a politics professor of the Moscow State Institute of International Relations, said regional cooperation in the search for MH370 was impressive.

Chris McLaughlin, senior vice president of Inmarsat, agreed the persistent and close cooperation among countries involved in the search was impressive.

In addition to government efforts, many companies and organizations such as Inmarsat also played an active role and made their contribution to the search, he said.

The Boeing company, which built the missing aircraft, said in a statement Thursday it was engaged as technical adviser to the U.S. National Transportation Safety Board, sharing technical expertise and analysis with the Malaysian investigation team and supporting the ongoing search.

"We are working with all parties in hopes of bringing this to a resolution as soon as possible," it said.

Angus Houston, chief of the Australian Joint Agency Coordination Center (JACC), said all parties had "worked together closely" in the search.

"Australia and PRC, together with Malaysia and other nations, have worked tirelessly in trying to find flight MH370," he said.

In an emailed statement issued Wednesday, U.S. Navy 7th Fleet Commander Vice Admiral Robert Thomas said support from U.S. allies and partners in the region had been "exceptional."

"At one point, 26 countries were working together in close coordination to achieve a common goal," he said. "To see such significant depth of international cooperation coming together for one mission is unprecedented and highly encouraging for the security and stability of the region."

Oh Ei Sun, senior research fellow at Singapore Rajaratnam School of International Studies and former political secretary to the Malaysian prime minister, agreed cooperation and coordination in humanitarian and non-traditional areas were increasingly important. "It is heartening to see those participating countries are sharing information and sometimes even resources, all with humanitarian aims," he said.