DAKAR, Sept 1 (Reuters) - The second phase of Senegal's Greater Tortue Ahmeyim (GTA) gas project will need investments worth around $5 billion and could start in 2024 or 2025, Senegal's President Macky Sall said on Thursday.

BP (BP.L) and U.S.-listed Kosmos Energy (KOS.N) are leading the development of GTA and Yakaar-Teranga, Senegal's first natural gas projects.

The first phase of GTA, which straddles the border between Senegal and Mauritania, is 80% complete and expected to start delivering gas by the end of 2023.

"In the Phase 2, that will come immediately after Phase 1, we expect to produce 5 million tonnes of gas compared with Phase 1, with the target of hitting 10 million tonnes of gas," Sall told a conference.

A Floating Production Storage and Offloading (FPSO) is expected to sail from China to the site by the end of the year, BP Executive Vice-President for Production and Operations Gordon Birrell told the same conference earlier on Thursday.

BP (BP.L) is in discussions with Senegal and Mauritania about GTA's phase two and other projects in both countries, Birrell said without elaborating.

"We are also working with the government of Mauritania on the most attractive development path for the BirAllah gas (field)," he said.

"With the government here (in Senegal) we are in deep dialogue in exploring the development of a national gas-to-domestic power project called Yakaar," Birrell added.

Another long-awaited oil and gas project, Sangomar, is also expected to begin production in the second half of next year.

Australia's Woodside (WDS.AX) holds 82% of the field being developed off the coast of Senegal and the national oil company Petrosen the rest.

Woodside Executive Vice-President for International Operations Shiva McMahon, told the conference the project was 60% complete.

Sall said Sangomar's Phase 2 would require investments worth $2.5 billion and was expected to produce around 100,000 barrels per day. He did not give a timeline for the second phase.