Cameron announced the new funding earlier this week as he began his visit to Jamaica, which focused on reinvigorating the relationship between the UK and Caribbean countries.
He said the UK wanted to help Caribbean countries develop by supporting economic growth.
“That’s what this £300m infrastructure fund is all about,” the British prime minister said.
“It will help to fund upgrades to ports, new roads and new bridges – making it easier here for businesses to trade with one another and with the rest of the world. And it will help benefit British businesses too who have the knowledge and expertise to deliver the infrastructure improvements needed.
“It makes the United Kingdom one of the largest bilateral donors to the region – concrete proof of our determination to reinvigorate this relationship.”
International Development Secretary Justine Greening added that too many Caribbean countries had been held back because they remain vulnerable to severe economic and climate shocks.
Greening said: “With some of the highest energy costs in the world, it is difficult for businesses to compete in global markets, leading to decades of slow or declining growth.”
The infrastructure fund has been delivered in collaboration with the Caribbean Development Bank.