Japanese Prime Minister Shinzo Abe on Thursday expressed concern over excessive debt in Africa, a veiled reference to what critics call China's "predatory" lending practices on the continent.

"You cannot invest in a country that is saddled with debt," Abe said in remarks opening the second day of the Tokyo International Conference on African Development, being held in the port city of Yokohama near the capital.

Japan will provide training in debt and risk management to 30 African countries over the next three years to facilitate economic growth on the continent, he said.

China has been accused of providing large loans under its Belt and Road infrastructure development initiative to developing countries that are ill-equipped to pay them off.

According to Japanese government sources, a joint declaration to be adopted after the conference wraps up on Friday will touch on the issue.

The seventh TICAD is being attended by leaders and representatives from more than 50 African nations and international organizations as well as companies from Japan and Africa.

Discussions in a plenary session on Thursday morning focused on cooperation between the public and private sectors on development in Africa, whose population is projected to reach 2.5 billion in 2050, or a quarter of the global population.

"The African market is seeing continuous growth. The day is close when the entire continent will become a huge economic bloc," Abe said.

Egyptian President Abdel Fattah el-Sisi, who is co-chairing the three-day conference along with Abe, said companies need to play a bigger role in ensuring Africa reaches its potential.

"The achievement of a robust economic start is no longer the responsibility of governments alone. It entails finding a constructive partnership with the private sector as the main growth engine, side by side with the powerful role of the state as a supporter, regulator and catalyzer for the economy," he said.

At a related forum held by the Japan External Trade Organization, Abe said there is increasing demand in Africa for overseas capital.

"There has been a rapid increase in investment, especially from emerging economies. Now is the time for Japanese companies to answer the call and take advantage of this opportunity," Abe said. "The Japanese government will do its utmost to provide support."

Abe has said Japanese companies will invest more than $20 billion in Africa over the next three years, and pledged to make basic medical care accessible to an additional 3 million people as part of his country's efforts to support development on the continent.

At a plenary session in the afternoon focusing on the sustainable use of ocean resources under the concept of a "blue economy," Japanese Foreign Minister Taro Kono said his country will help in human resource development for 1,000 people in fishery, port facility management and maritime security over the next three years.

"I am convinced that blue economy is in complete accordance with Japan's vision of a free and open Indo-Pacific," he said, referring to a strategy the country has pushed to counter China's growing assertiveness in the East and South China seas.

TICAD, which is co-hosted by the Japanese government, the United Nations, the World Bank, the U.N. Development Program and the African Union Commission, had been held every five years from 1993 until its fifth session in 2013, when it switched to being held every three years.

On Thursday, Abe held bilateral meetings with more than a dozen African leaders on the sidelines of the conference, including Ethiopian Prime Minister Abiy Ahmed and Ugandan President Yoweri Museveni.