Presidents and prime ministers as well as foreign ministers and ambassadors from more than 40 countries signed the world's first nuclear weapons ban treaty on Wednesday after it was opened at a ceremony with Japanese atomic bomb survivors and the Mayor of Nagasaki in attendance.

The United Nations anticipates that by day's end, the number of countries endorsing the pact could rise to 51.

This is the follow-up to the historic adoption of the treaty on July 7, when 122 countries voted in favor of pursuing a nuclear-free world by banning atomic weapons for the first time after decades of prodding by atomic bomb victims, known as hibakusha in Japanese, and civil society.

"The treaty is an important step towards the universally-held goal of a world free of nuclear weapons. It is my hope that it will reinvigorate global efforts to achieve it," U.N. Secretary General Antonio Guterres said at the opening ceremony. "Today we rightfully celebrate a milestone. Now we must continue along the hard road towards the elimination of nuclear arsenals."

The event occurs against the backdrop of uncertainty as North Korea continues marching forward in its quest for operational nuclear weapons. It also comes a day after U.S. President Donald Trump warned North Korea in the General Assembly hall that "We will have no choice but to totally destroy North Korea" if his country or its allies are threatened.

The treaty's backers believe that their path is the best option to prevent future nuclear catastrophes of the kind experienced by Japan in 1945 during the closing days of World War II. The bombings of Hiroshima on Aug. 6 of that year and Nagasaki three days later ushered in the nuclear era.

"The heroic survivors of Hiroshima and Nagasaki -- the hibakusha -- continue to remind us of the devastating humanitarian consequences of nuclear weapons," the U.N. chief added.

Also speaking was Peter Maurer, president of the International Committee of the Red Cross, who said the organization received a cable from Hiroshima on Aug. 30, 1945 describing a "city wiped out," a great number of dead and over 100,000 wounded.

"The world today needs the promise of this treaty: the hope for a future without nuclear weapons," he said. "Humanity simply cannot live under the dark shadow of nuclear warfare, and the immense suffering which we all know would result."

Brazilian President Michel Temer was the first to sign as the highest-ranking politician from the country that came first in alphabetical order. He was followed by more than 40 other leaders representing countries in Asia, Africa, Europe, the Caribbean and South America, as well as Pacific Island nations, including Fiji, whose citizens have been victims of nuclear testing.

The Holy See, Guyana and Thailand also submitted their instruments for ratification during the morning event. The treaty goes into effect 90 days after 50 nations have ratified it.

Notably absent were the five permanent U.N. Security Council seat holders -- Britain, China, France, Russia and the United States -- who all possess the destructive devices.

Nuclear umbrella nations, such as Japan and South Korea, and North Atlantic Treaty Organization members like Germany and The Netherlands did not endorse it either.

These countries oppose the ban treaty in favor of the Nuclear Nonproliferation Treaty, which many criticize for falling short of ridding the world of nuclear weapons since it entered into force in 1970. Critics point out that, contrary to the goal of denuclearization, states with nuclear weapons have only continued to modernize their arsenals.

"Although we share the same feelings about nuclear abolition, (the treaty) differs from Japan's approach, so we will not be signing it," Japanese Foreign Minister Taro Kono told reporters in New York.

"Unfortunately, the reality is that there are divisions between countries with nuclear weapons and those without, as well as between the countries without them, when it comes to recognizing (both) the inhumanity of nuclear weapons and the severity of the security environment," he said, adding that Japan will try to bridge those gaps through existing frameworks.

Some of the permanent Security Council members, such as the United States, have been pressing nations that backed the treaty to refrain from signing it, according to Beatrice Fihn, executive director of the International Campaign to Abolish Nuclear Weapons.

Officials from some countries that signaled their intentions to sign the ban have been called into meetings in capitals around the world, she explained. They also received other forms of communication discouraging them from signing on.

This particularly raises concerns about smaller countries that could be influenced, diplomats have said.