African leaders agreed on Wednesday to form a $3 trillion continental free-trade zone encompassing 1.2 billion people.

But its two biggest economies, Nigeria and South Africa, did not sign up, diminishing its impact.

The African Union started talks in 2015 to establish a 55-nation bloc that would be the biggest in the world by member states, in a bid to increase intra-regional trade, which sits at a measly 15 per cent of Africa's total commerce.

Rwandan president Paul Kagame, host of an AU summit called to conclude the initial negotiations, declared the meeting a success after 44 African nations signed up to establish the free trade bloc within 18 months.

In a statement, the Nigerian government said that "certain key stakeholders in Nigeria indicated that they had not been consulted, for which reasons they had some concerns on the provisions of the treaty".