He added that Africa's least developed, heavily indebted and poor countries will be exempt from debt they have incurred in the form of interest-free Chinese loans due to mature by the end of 2018.
The goal of the 2018 FOCAC meeting is the promotion of economic and trade cooperation between China and African economies.
Xi said China would set up a China-Africa peace and security fund and that a total of 50 "security assistance" programs will be carried out, such as United Nations peacekeeping missions, fighting piracy and combating terrorism.
Chinese companies will be encouraged to invest no less than $10bn in the continent in the next three years, he added.
Xi's announcement followed China's decision to contribute $60 billion in investments three years ago, the news agency reported.
Al Jazeera's Adrian Brown, reporting from Beijing, said economists and some worldwide financial institutions worry that Chinese loans are burying some countries under massive debt.
Ghana and a dozen others signed agreements before the start of the summit for China to build more roads, develop the aviation sector, improve healthcare delivery and many more projects in their countries.
China loaned around $125 billion to the continent from 2000 to 2016, data from the China-Africa Research Initiative at Washington's Johns Hopkins University School of Advanced International Studies shows.
Apart from military aid to the African Union, Beijing will support countries in the Sahel region and others bordering the piracy-ridden Gulf of Aden and Gulf of Guinea.
President Cyril Ramaphosa has called on the Chinese communist party to work more closely with the ANC.
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Addressing the summit, Rwandan President and African Union chairman Paul Kagame said a stronger Africa was an opportunity for investment, "rather than a problem or a threat".
It is the only African state to maintain diplomatic ties with Taiwan.
Meanwhile the exiled leader of the opposition in the Maldives, Mohamed Nasheed, has said China's actions in the Indian Ocean archipelago amounted to a "land grab" and "colonialism", with 80 per cent of its debt held by Beijing.
Speaking earlier in the day, Xi said China's investments on the continent have "no political strings attached".
The participants are looking for ways to "advance common growth and development", said South Africa's foreign minister, Lindiwe Sisulu.
All but six of the over 40 African leaders and heads of state and government attended the 3rd Summit chaired by the Communist leader Xi Jinping to definitely tighten China's grip over Africa and to deepen Africa's dependency on China.
He was accompanied to Beijing by his wife, Aisha, who is scheduled to participate in a spouses" programme on China-Africa at the Great Hall of the People, with the theme: "Joining Hands for a Future of AIDS' and one of his daughters.
China has been Africa's biggest trading partner for the last nine years, with trade volume growing 14 per cent to US$170 billion last year.
He pointed out that energy, transport, telecommunications and tapping cross-border water resources would be on China's radar in the next phase of Africa's infrastructural forays.