It is the first time that world leaders to attend such a high-level meeting to deliberate and commit to women and girls, said Mlambo-Ngcuka, who was appointed as executive director of the UN Women by UN Secretary-General Ban Ki-moon in 2013.

"This is an opportunity to put the issue of women and girls on the top of agenda of world leaders, and to keep it there until the time we have corrected with the leaders, with women's organizations, with civil society, with men and boys as well," said Mlambo-Ngcuka.

She listed such commitments the leaders are expected to make as curbed percentage of violence against women, and the amount and date of investment made to women entrepreneurs, among others.

This year marks the 20th anniversary of the Fourth World Conference on Women in Beijing and the adoption of the Beijing Declaration and the Platform for Action, a comprehensive roadmap for gender equality and women empowerment.

"The last 20 years did see progress," said Mlambo-Ngcuka, who was South Africa's first female deputy president from 2005 to 2008.

"In the area of legislation, many countries passed legislation that affirms gender equality; in the area of education, especially primary education, access and enrollment (of) girls increase phenomenally," she added.

According to the data by UN Women, developing countries have almost achieved gender parity in primary education; at least 50 percent of the world's women are in paid wage and salary employment, an increase from 40 percent in 1990; the percentage of women in parliament has nearly doubled in the last 20 years.

However, "progress has been slow and uneven," she pointed out.

Women worldwide are still faced with violence, poverty, lack of access to high education, relatively low representation in political as well as economic decision-making bodies, she said.

Statistics show that gender disparity widens at secondary and tertiary school level in many countries; women earn 10-30 percent less than men for the same work; only 22 percent of all national parliamentarians were female as of August 2015.

To address those issues, countries should implement the already passed legislation, continue to enact good legislation where there is a gender gap, and repeal bad ones that discriminate women, she urged.

"Countries also need to invest in gender equality," she said, citing affordable child care facilities as the one that countries can put their money in.

"Many women cannot go to work because of unpaid care work, like looking after children," she elaborated. "In that way (affordable child care facilities) would create changes that last because women always have somewhere to take the children to."