Construction has begun on a $23bn (£14.5bn) port project and oil refinery in south-eastern Kenya’s coastal Lamu region near war-torn Somalia’s border.
An oil pipeline, railway and motorway will also be built linking Lamu to South Sudan and Ethiopia.
Newly independent South Sudan plans to use Lamu as its main oil export outlet.
A BBC reporter says security concerns for the project may explain the presence of Ethiopian and Kenyan troops in Somalia aiming to pacify the region.
Kenya’s leader Mwai Kibaki launched the project along with his South Sudanese and Ethiopian counterparts, Salva Kiir and Meles Zenawi respectively.
“I have no doubt that this day will go down in history as one of the defining moments – when we made a major stride to connect our people to the many socio-economic opportunities that lie ahead,” AFP news agency quotes Mr Kibaki as saying at the inauguration ceremony.
Known as Lamu Port South Sudan Ethiopia Transport Corridor (Lapsset), it is expected to be completed within four years with initial costs coming from the three governments and plans to attract international investment.