Several financial institutions have been ordered by the Hong Kong Monetary Authority to carry out independent reviews of their foreign exchange trading operations amid growing suspicions of market manipulation.

The HKMA, Hong Kong's de facto central bank, was the first Asian financial regulator to open a probe into potential forex market rigging in October 2013. Other global regulators, from New York to London to Zurich, have also opened investigations into the daily $5tn (£3tn, €3.6tn) currency market.

"The reviews are in progress," an HKMA spokeswoman told Reuters in the statement, adding that it is working with other overseas banking regulators. The unnamed banks told to conduct reviews must send the results to the HKMA.

HKMA's announcement comes just a day after the Swiss competition regulator Weko opened a new probe into allegations of forex fixing aimed at several major banks.

Weko claimed "evidence exists" that the banks under its investigation "colluded to manipulate exchange rates in foreign currency trades". Its investigation is not in conjunction with other regulators.

There are widespread concerns among regulators that traders at different banks conspired to manipulate key benchmark rates in the foreign exchange market.