The Japanese industrial and technology giant Toshiba has seen more than 40% of its stock market value wiped off since Monday (26 December), after the company warned that its US nuclear business may be worth less than previously thought.

Shares in Tokyo-listed company fell 12% on Tuesday, followed by declines of 20% on Wednesday and another 17% at the close of trading in Thursday (29 December).

Earlier in the week, Toshiba revealed that it is facing the prospect of a hefty one-off loss at its US nuclear industry subsidiary Westinghouse Electric, which it bought in 2006.

Much of problem stems from Westinghouse Electric's acquisition of nuclear construction outfit Chicago Bridge & Iron (CB&I) in 2015.

Auditors have ascertained that CB&I's assets could be worth less than their last valuation, atop ongoing disputes about payments and other factors driving up the costs of projects the outfit is handling in the US states of Georgia and South Carolina.

A spokesman for Toshiba said the size of the writedown at Westinghouse Electric might not be established until February. Its parent holding company Toshiba Nuclear has not made a profit since 2013.

According to Tokyo Shimbun the Toshiba writedown is expected to run into several billion dollars, while the revelation has also triggered a ratings downgrade of the company by Moody's and S&P. Toshiba president Satoshi Tsunakawa has since apologised for "causing concern" to investors.

The company was still in the nascent stages of its recovery from a 2015 accounting scandal, after investigations uncovered that headline profits had been overstated for seven years, prompting the departure of several senior managers, including Toshiba chief executive and then president Hisao Tanaka.

Until details of the problem emerged on Monday, Toshiba had been on course towards becoming the second biggest gainer on the Nikkei 225 for 2016; up more than 71% on an annualised basis. However, declines noted over the last three trading sessions have lowered those gains to around 4.8%, and it could get worse still.