Japanese technology giant SoftBank raised a record amount for its mobile unit in the world's second-biggest ever IPO but the shares plunged in a disappointing debut trading session.

A spokesman for the firm confirmed it had raised around 2.65 trillion yen ($23.5 billion) via the unit's IPO.

This makes it Japan's largest and the second-biggest globally after Alibaba went public in 2014.

But the stock opened at 1,463 yen, significantly lower than the initial offer price of 1,500 yen per share, and headed lower from there.

The shares finished the session at 1,282 yen, down 14.5% from the IPO price with heavy selling into the close.

Analysts said the IPO had not come at a particularly good time for the new company, named SoftBank Corp, as global markets have been suffering in recent months and Japan is taking aim at what they see as mobile operators' overly high prices. 

Other market players said tepid demand was not helped by an embarrassing episode earlier this month when a technical glitch left tens of millions of SoftBank and UK mobile phone operator O2 customers unable to access data. 

Add to that global security concerns over China's Huawei and "the number of those who wanted to buy the shares was rather small", analysts said.

SoftBank took more than one-third of its mobile unit public and was able to sell the full offering of 1.76 billion shares at the IPO price of 1,500 yen, beating the previous national records set by NTT in 1987 and its subsidiary NTT Docomo in 1998.

The blockbuster IPO is seen as part of boss Masayoshi Son's strategy of transforming SoftBank from a Japan-based telecom company to a global hi-tech investment firm.

Son has already said the IPO would go towards swelling the coffers of his SoftBank Vision Fund, which is worth an estimated $100 billion and has taken stakes in some of the hottest tech firms, including Uber, Slack, WeWork and Nvidia.

SoftBank and Son have come under the spotlight recently as nearly half the money in the fund comes from Saudi Arabia and the firm maintains close ties with the kingdom.

Those links were highlighted after the murder of journalist Jamal Khashoggi at the Saudi consulate in Istanbul, which sent shares in SoftBank spiralling.

Last month, in eagerly awaited comments on the scandal, Son condemned the killing but said he would continue to do business with Saudi Arabia.

Analysts at S&P Ratings have said the IPO "would further underline SoftBank's transition to an investment holding company".

Another ratings agency, Moody's, said the IPO would "enhance transparency" in the parent company's investment portfolio because the mobile unit's "share price and daily market value will be available to the public".

The SoftBank parent company itself has said the listing would give the mobile unit "greater managerial autonomy to develop its own growth strategy".

It has also said the listing would help clarify the roles of the parent company and its mobile unit.

The mobile unit said in a statement alongside the market debut that it expects net profit of 420 billion yen on sales of 3.7 trillion yen for the full year to March 2019.

In the year that ended March, it has logged net profit of 400.75 billion yen on sales of 3.58 trillion yen, it said.