The Philippine peso in September suffered the largest monthly loss in 16 years as concerns grew that President Rodrigo Duterte's policies may keep driving foreign investors out of the country.

The peso on Friday fell 0.4 percent to close at 48.50 per dollar, the weakest since September 2009.

The loss extended the currency's September slump to 4 percent, the largest monthly depreciation since October 2000.

Earlier on Friday, Duterte appeared to liken himself to Nazi leader Adolf Hitler and said he would "be happy" to exterminate three million drug users and peddlers in the country.

Duterte was voted to power in a May election on the back of a vow to end drugs and corruption in the country of 100 million people. He took office on June 30 and over 3,100 people have been killed since then, mostly alleged drug users and dealers, in police operations and in vigilante killings.