SINGAPORE - Trading in the shares of beleaguered commodity trader Noble Group were halted on Tuesday morning (May 23), after they plunged on opening, prompting a query from the Singapore Exchange.

Around 9:36am, the company requested an immediate trading halt, pending release of an announcement.

Its shares by then had sunk as much as 32 per cent to 40 Singapore cents, the lowest since 2001.

Earlier, at about 9:22am, SGX issued a query on the the stock's "unsual price movements".

Around 9:36am, the company requested an immediate trading halt, pending release of an announcement.

Noble's latest share dive came after S&P Global Ratings on Monday cut its long-term corporate credit rating on Noble three notches to CCC+ from B+, warning that the once-blue chip company could default on its debt over the next year.

"The negative outlook on Noble reflects the potential that the company will face distress and a non-payment of its debt obligations over the next 12 months," S&P said in a statement after trading closed on Monday. Its warning comes on the heels of downgrades from Moody's Investors Service and Fitch Ratings.

Also on Monday, wire agency Reuters reported during trading hours that China's state-owned Sinochem Group was no longer interested in making an investment in Noble, sending its shares down 6.4 per cent for the day, and its bonds due in 2022 down 14 per cent.

Since announcing a surprise US$129 million quarterly loss two weeks ago, Noble shares have tumbled to 16-year lows and the price of its bonds has fallen by more than half.

Its market value has shrunk to a low of about US$400 million from US$6 billion in February 2015, said Reuters