HANOI, July 14 (Reuters) - Shareholders of Black Spade Acquisition, a special purpose acquisition company (SPAC) that has plans to merge with Vietnam's electric automaker VinFast to allow a U.S. listing, have redeemed over 80% of their shares, the company said on Friday.

The move represents a new setback for the startup, which had initially planned a U.S. listing on its own and has struggled to start production and ramp up sales outside Vietnam.

The Hong Kong-based SPAC's shareholders have not yet voted on the proposed merger with VinFast, but have exercised their right to redeem shares by Tuesday this week.

Black Spade Acquisition (BSA) said that redemptions amounted to approximately $147 million. "Following the redemption (...), the amount of funds remaining in the trust account is approximately $28.56 million," the SPAC said in a statement.

NYSE-listed BSA was founded by the private investment arm of Lawrence Ho, the son of gambling mogul Stanley Ho. As the SPAC's planned timeframe for striking a deal drew towards its end, BSA announced in May a surprise merger plan with VinFast to list the carmaker in the New York Stock Exchange.

The SPAC had initially sought to merge with a company ideally in the entertainment business, according to its website.

In a new twist, a month later BSA delisted from NYSE and joined the secondary NYSE American, a market for smaller-cap companies that has tended to have lower liquidity.

VinFast, which was founded in 2017 and began selling electric vehicles in California this year, previously filed for an initial public offering in the U.S. to list on the Nasdaq under ticker symbol "VFS" in December last year, aiming for a valuation of about $60 billion.

The company did not immediately reply to a request for comment.

The new merged entity was estimated by VinFast and BSA to have a potential equity value of $23 billion.

On Thursday, the SPAC's remaining shareholders voted to extend its lifespan by one year, about a week before the end of its original two-year term.

BSA had no immediate additional comment. (Reporting by Francesco Guarascio @fraguarascio, Phuong Nguyen and Kevin Krolicki Editing by David Evans and Mark Potter)