World leaders on Monday vowed solidarity and support for the World Health Organization, or WHO, in fighting COVID-19 while learning lessons from the response to the global pandemic.

The 73rd annual World Health Assembly is the first virtual version in its history, bringing the representatives from the WHO's 194 member states together online.

The novel coronavirus has infected more than 4.5 million people and killed more than 300,000 while causing huge damage to the global economy.

United Nations Secretary General Antonio Guterres said the challenge of handling COVID-19 must be a wake-up call.

"It's time for an end to the hubris. Our deep feeling of powerlessness must lead to greater humility. Deadly global threats require a new unity and solidarity," he told the assembly.

While there has been some solidarity, there was very little unity in the response, he said. "Different countries have followed different, sometimes contradictory, strategies and we are all paying a heavy price," he said.

He said many countries have ignored the WHO recommendations and as a result, the virus has spread and is now moving into the global South, where its impact may be even more devastating.

He urged the G20 to consider the urgent launch of a large-scale, coordinated and comprehensive stimulus package amounting to a double-digit percentage of global GDP.

"The global North cannot defeat COVID-19 unless the global South defeats it at the same time," Guterres said.

Guterres said that once the world has finally turned the page on the pandemic, there must be a time to look back fully to understand how such a disease emerged and spread its devastation so quickly across the globe and how all those involved reacted to the crisis.

"The lessons learned will be essential to effectively address similar challenges, as they may arise in the future,"

"But now is not that time. Now is the time for unity, for the international community to work together in solidarity to stop this virus and its shattering consequences.

"Either we get through this pandemic together, or we fail," Guterres said.

WHO Director-General Tedros Adhanom Ghebreyesus said the COVID-19 pandemic has brought out the best and worst of humanity.

"Fortitude and fear; solidarity and suspicion; rapport and recrimination. This contagion exposes the fault lines, inequalities, injustices and contradictions of our modern world," he said.

He said that the WHO "has stood shoulder-to-shoulder with countries in these darkest of hours" and every country and every organization must examine its response and learn from its experience.

Tedros said that he will initiate an independent evaluation at the earliest appropriate moment to review experience gained and lessons learned, and to make recommendations to improve national and global pandemic preparedness and response.

German Chancellor Angela Merkel said that since virtually no country has been spared by the pandemic, no country can solve the problem alone.

"We must work together," she said.

Merkel said that the WHO is the legitimate world organization for the area of health, adding that the world should continue to work to improve procedures within the WHO and look at its financing to ensure it is sustainable.

The US government has halted most of its funding to the WHO, drawing widespread condemnation from the world.

"I am convinced that we will be able to overcome this pandemic when we work together, and that will help us to achieve this more rapidly," Merkel said.

South African President Cyril Ramaphosa said that the pandemic has highlighted the dangerous and growing inequality that exists between countries and within them.

"Africa is extremely vulnerable to the ravages of this virus, and needs every possible support and assistance," said Ramaphosa, who is also chair of the African Union. Africa affirmed its full support for the WHO, which has been key in guiding the international response to the pandemic.

South Korea President Moon Jae-in said that to safeguard the health of the humanity, his country will continue to work closely with the WHO.

"In the face of crisis, humankind must choose solidarity and cooperation over the pursuit of individual interests. The world must unite under the banner of mutual trust and inclusiveness in the face of deepening crisis," he said.

French President Emmanuel Macron called the 73rd WHA as the most important assembly in the history of WHO.

"It must be a moment for unity and a moment for solidarity, but also a moment for clear thought and action in the face of what is an unprecedented global crisis affecting all of us," he said.

He expressed that "we cannot let ourselves be divided".

"Our absolute priority, the only priority we are talking about, is to conquer this pandemic," he said.

"As long as the disease remains a threat to a few, it will remain a threat for everybody," Macron said, echoing the message by many at the assembly.