KUNMING - The number of confirmed dengue fever cases rose to 257 in a prefecture of southwest China's Yunnnan Province as of Saturday afternoon, local authorities said.

There have been no deaths reported since the disease was first reported in the area on August 15, according to the information office of the Dai Autonomous Prefecture of Xishuangbanna.

The cases included six originating from overseas.

Of the confirmed cases, 96 were hospitalized and the others were being treated at home or in clinics. A total of 19 have left hospital after treatment.

Dengue is a mosquito-borne, potentially fatal disease that affects between 50 and 100 million people in tropical and subtropical regions every year, causing fever and muscle and joint aches.