SoftBank Corp shares slumped more than 10 percent in their debut on Wednesday, as investor appetite for Japan's biggest ever IPO was hurt by a recent major service outage and worries over its exposure to Chinese telecom gear maker Huawei.

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Following its $23.5 billion initial public offering, shares of the telecoms unit of SoftBank Group Corp fell as far as 1,344 yen five minutes into trade, or 10.4 percent lower than its IPO price of 1,500 yen. The broader Tokyo market was down 1.0 percent.

At 9:27 a.m. (0027 GMT), the shares were at 1,367 yen, after opening at 1,463 yen. SoftBank Group was down 2.7 percent.

SoftBank Corp CEO Ken Miyauchi will hold a news conference at 0630 GMT.

The IPO was just shy of the world record $25 billion 2014 listing of Chinese e-commerce giant Alibaba Group Holding Ltd, a SoftBank Group portfolio company.

During the IPO period, Japan's third-largest mobile phone network provider by subscriber numbers suffered a rare nationwide service outage, which it said would not affect earnings or dividends.

Adding to investor worries, SoftBank Corp's relationship with Huawei Technologies Co Ltd came under scrutiny as governments around the world moved to shut out the Chinese firm amid worries its gear could facilitate Chinese spying.

SoftBank Corp, which has the most exposure to Huawei among Japanese telecoms firms, plans to replace Huawei-provided 4G network equipment with other suppliers' hardware, two sources said, in a process likely to be time-consuming and expensive.