(Adds quotes, details of Sunseap's business)

SINGAPORE/LISBON, Oct 26 (Reuters) - Energias de Portugal is in advanced talks to buy a majority stake in Sunseap Group in a deal that will value the Southeast Asian renewables company at around S$1 billion ($742 million), three sources with knowledge of the matter said on Tuesday.

EDP Renovaveis (EDPR), 75% owned by EDP, Portugal's biggest utility, is in late-stage talks to buy the stake held in Sunseap by Thai energy firm Banpu PCL, Singapore state investor Temasek Holdings, a Temasek-backed fund and other investors, the sources said.

EDPR's move to snap up the solar energy group reflects the world's fourth largest renewable energy producer's ambition to accelerate its growth in Asia.

Banpu holds a nearly 49% stake in Singapore-based Sunseap through a subsidiary, which it has built up since its initial investment in the group in 2017. Details of stakes held by other shareholders have not been made public.

Two of the sources said EDPR is seeking to own a significant majority in Sunseap and is also considering investing at least $1 billion in the company's business over the next few years.

The sources declined to be identified due to confidentiality constraints. EDP, Banpu, Sunseap and Temasek all declined to comment.

"Although the deal is not yet closed, negotiations are at a very, very advanced stage," said one industry source.

"This deal would allow EDPR to achieve a strong presence in solar energy in Asia, which is something it has been studying for a long time," he said.

Sunseap also counts Japanese firms and other companies among its investors.

Decade-old Sunseap is now a regional solar energy system developer, owner and operator, with more than 2,000 megawatt-peak of solar energy projects contracted across Asia. It operates across Southeast Asia, China, Taiwan and Japan. ($1 = 1.3483 Singapore dollars) (Reporting by Anshuman Daga and Roslan Khasawneh in Singapore and Sergio Goncalves in Lisbon; Editing by Jan Harvey and Jane Merriman)