JAKARTA, June 16 (Reuters) - Indonesian e-commerce firm Bukalapak is keen to raise as much as $800 million in an IPO in August, two people with knowledge of the matter said, the first of two big tech listings in Jakarta this year that will add long-sought lustre to the local bourse. A mid-year debut could see it become Indonesia"s biggest listing in 10 years and the largest ever for the country by a startup. But those milestones will likely later be overtaken by the planned listing of GoTo - a new company to be formed by the merger of e-commerce rival Tokopedia and ride-hailing and payments firm Gojek. Tapping a sharp pickup in investor interest in Southeast Asia"s rapidly expanding technology sector, Bukalapak, the country"s No. 4 e-commerce firm, is aiming to sell 10% to 15% of the company and wants a valuation of between $4 to $5 billion, the people said. A confidential listing prospectus has been submitted to the Indonesia stock exchange, one of the sources added. Proceeds from the offering could range between $500 million and $800 million depending on investor demand and market conditions, according to the sources who were not authorised to speak on the matter and declined to be identified. Bukalapak, which said in 2019 it was valued at more than $2.5 billion, declined to comment. The 11 year-old startup which claims to have more than 100 million users has a plethora of big-name investors backing it including Microsoft (MSFT.O), Singapore sovereign wealth fund GIC, local media conglomerate Emtek (EMTK.JK), the investment arm of Standard Chartered [RIC:RIC:STANB.UL] and South Korean web portal Naver Corp (035420.KS). Bukalapak was originally aiming to raise $300 million from its domestic listing before looking to merge with a special purpose acquisition company (SPAC) in the United States but it is now focusing solely on its IPO, one of the sources said. The listing, which sources say is set to take place mid-August, is a victory for Indonesia"s bourse which has been conducting an extensive charm offensive to convince the country"s thriving startups to list locally instead of heading to the United States. Stagnant for many years, Indonesia"s total IPO deal value took a further hit during the coronavirus pandemic, more than halving in 2020 to $470 million, according to Refinitiv data. So far this year, 15 companies have raised a combined $125 million via IPOs. One key change will be the imminent amending of listing rules to allow non-profitable companies to go public, sources have told Reuters. With a population of 270 million, Southeast Asia"s largest economy has one of the fastest-growing online shopping sectors in the world. Indonesia"s e-commerce sector exceeded $40 billion worth of gross merchandise value in 2020, according to a June report by tech consultancy Momentum Works, which estimates that Bukalapak holds a 7% market share. To differentiate itself, Bukalapak has focused on expanding into offline services and into smaller cities in Indonesia, said Momentum Works founder Jianggan Li. That said, it still has a long way to go before it catches up to bigger rivals - Sea"s (SE.N) e-commerce arm Shopee, Tokopedia and Lazada, which is owned by China"s Alibaba Group Holding Ltd (9988.HK). "The competitive landscape of large e-commerce marketplaces in Indonesia is firming up, catalyzed by the pandemic, with the gaps between tiers of players widening," said Li.