Duterte on Tuesday announced the imposition of martial law in the region of Mindanao, home to about 20 million people, after terrorists who pledged allegiance to the ISIS rampaged through a city there.
Duterte said he was considering also imposing martial law through the central third of the Philippines known as the Visayas, because this region is very close to Mindanao.
He then also raised the prospect of the northern third of the Philippines, known as Luzon and home to the capital of Manila, falling under martial law.
"If I think that the ISIS has already taken foothold also in Luzon, and terrorism is not really far behind, I might declare martial law throughout the country to protect the people," he said.
Duterte warned martial law would be similar to military rule imposed by dictator Ferdinand Marcos a generation ago.
Marcos's two-decade rule ended in 1986 when millions of people took to the streets in a famous "People Power" revolution.
"Martial law of Mr Marcos was very good," Duterte said.
Duterte said his own version of martial law meant security forces could conduct searches and arrest people without warrants.
He also said there would be curfews for some provinces in Mindanao.