Several witnesses told Dow Jones Newswires that at least three explosions were heard around the Mega Kuningan business area where the JW Marriott and Ritz Carlton hotels and some foreign embassies are located.

"I heard at least three explosions and now white smoke is billowing," a fund manager at a foreign securities company told Dow Jones Newswires on the phone.

It remains unclear what caused the explosions.

Another witness said that some of the buildings in the area are being evacuated.