SINGAPORE (BLOOMBERG) - Trade with caution.

That's the message from Singapore's regulator to investors in the Singapore Exchange Ltd, which jumped Wednesday by the most since July 2009. It's the first time the bourse operator has been the subject of such an alarm; the bourse itself has dished out the warning on more than 50 companies since the introduction of tougher rules in March 2014.

The Monetary Authority of Singapore has regulatory oversight over SGX, while also working with it to monitor the rest of the city's listed companies. Two trading disruptions last year earned SGX a reprimand and a bar on raising fees until fixes are made. Shares in Southeast Asia's biggest exchange operator jumped 4.5 per cent on Wednesday, and the company said it didn't have a reason for the rally.

"Shareholders and potential investors should exercise caution when dealing in the securities," MAS said in a statement on Thursday. "MAS will investigate all possible transgressions and pursue all actions necessary to maintain a fair, orderly and transparent market."

SGX slipped 0.4 per cent as of 10:59 a.m. in Singapore, paring its 2015 gain to 4.4 pe rcent. SGX shares have underperformed, so may have jumped on buying from just one or two fund managers, according to Nicholas Teo, a strategist at IG Ltd. in Singapore.

"This extra policing by the regulator may have the unintended consequence of hampering trades and preventing the creation of a more vibrant market," Teo said. "I think it's a bit too much."

SGX was valued Wednesday at 22.5 times estimated earnings, compared with Hong Kong Exchanges & Clearing Ltd.'s multiple of 35 times.