Day-one buying exceeds US retail demand by more than fivefold People gather to watch a live feed with SpaceX CEO Elon Musk on the day of SpaceX's initial public offering at the Nasdaq MarketSite in New York City on Friday. Reuters-Yonhap South Korean retail investors snapped up more than 1 trillion won ($661 million) worth of SpaceX shares on the company's stock market debut, underscoring the intense local appetite for the Elon Musk-led space firm.It is rare for a single US-listed stock to attract more than 1 trillion won in net buying from Korean retail investors in a single session, making SpaceX one of the biggest overseas stock purchases by Korean retail investors in recent years.According to financial industry sources Wednesday, Korean retail investors bought a net 1.2 trillion won worth of SpaceX shares on June 12, the first day of trading, through 11 brokerages, including Mirae Asset Securities, Korea Investment & Securities and Toss Securities.The buying dwarfed retail demand in the US market. According to Vanda Research, US retail investors purchased a net $117 million to $118 million worth of SpaceX shares on the first trading day. Although many US investors received IPO allocations directly, Korean retail investors still purchased more than five times as much SpaceX stock in the secondary market.The buying spree dwarfed demand for other overseas securities. The day's second-most purchased asset among Korean investors, the ProShares UltraPro QQQ ETF (TQQQ), recorded net purchases of just $24.9 million.Before SpaceX's debut, the most heavily bought overseas security this month had been the Direxion Daily Semiconductors Bull 3X Shares ETF (SOXL), which attracted net purchases of $514.2 million on June 4. SpaceX surpassed that figure on its first trading day alone, drawing more than $660 million in net buying.SpaceX shares were priced at $135 in the IPO and opened at $150. The stock climbed as high as $176 before closing at $161.11, up 19.3 percent from the offering price. Based on the first day closing price, Korean retail investors are estimated to have accumulated roughly 5 million shares.Momentum continued after the debut. SpaceX gained another 19.6 percent on June 15, its second trading day. Net purchases by Korean retail investors over the first two trading sessions are expected to exceed 2 trillion won.The scale of the buying highlights how quickly SpaceX has become a core holding among Korean retail investors. The company vaulted into the ranks of the 30 most widely held US stocks after just one trading session, joining a group traditionally dominated by Big Tech names such as Nvidia, Tesla, Apple, Microsoft and Alphabet.