The Treaty on the Prohibition of Nuclear Weapons -- which bans the use, development, production, testing, stationing, stockpiling and threat of use of such weapons -- was adopted by the UN General Assembly in July 2017 with the approval of 122 countries.

Since then, 84 states have signed the treaty, which will come into force 90 days after 50 of those signatories ratify the document.

The 75th anniversary of the nuclear bomb attacks on Nagasaki and Hiroshima, marked in August, has seen a wave of countries ratify in recent months.

They include Nigeria, Malaysia, Ireland, Malta, and most recently Tuvalu on October 12, bringing the number up to 47.

A 48th country is expected to ratify in the coming days, with others thought to be on the brink of doing likewise within weeks.

"This is a really big deal that the treaty is about to enter into force," said Beatrice Fihn, the executive director of the International Campaign to Abolish Nuclear Weapons (ICAN).

"It could be in a matter of days. It's really quite imminent, we think."

ICAN, a coalition of non-governmental organisations, won the 2017 Nobel Peace Prize for its key role in bringing the treaty to fruition.

- 'Historic milestone' -

"That these countries have done this, despite the pandemic and enormous pressure from nuclear-armed states, is really quite impressive," Fihn told reporters at the United Nations in Geneva.

"This would be a really historic milestone. This treaty will complete the bans on weapons of mass destruction. It will stand next to the ban on biological weapons and chemical weapons."

Thailand, Mexico, South Africa, Bangladesh, New Zealand, Vietnam and the Vatican are among the countries who have already ratified the treaty.

The clutch of nuclear weapons-possessing states, including the United States, Britain, France, China and Russia, have not signed the treaty.

However, campaigners hope that it coming into force will have the same impact as previous international treaties on landmines and cluster munitions, bringing a stigma to their stockpiling and use, and thereby a change in behaviour even in countries that did not sign up.

Nuclear-armed states argue their arsenals serve as a deterrent and say they remain committed to the nuclear Non-Proliferation Treaty, which seeks to prevent the spread of nuclear weapons.

Fihn said the surge of ratifications around the 75th anniversary of the Hiroshima and Nagasaki attacks came with states keen to see the treaty implemented within the lifetime of the last remaining survivors.

"They should see the day when nuclear weapons become banned," she said.