The emergency package includes low-cost loans, grants and technical assistance.
The action comes as leaders around the world pledge to shield their countries from the economic impact of the outbreak.
It follows warnings that slowdown from the outbreak could tip countries into recession.
The aid is intended to help countries improve their public health response to the crisis, as well as work with the private sector to reduce the economic impact.
"What we're trying to do is limit the transmission of the disease," World Bank Group President David Malpass told the BBC.
The organisation said it would prioritise the poorest and most at-risk countries in distributing the aid to counter the effects of the virus, which has spread to more than 70 countries around the world.
Half of the package comes from the bank's International Finance Corporation, which works with the private sector. About $4bn of the $12bn is being shifted from previously available funds.
More about: World-Bank coronavirus
