Duterte is widely expected to win approval for martial law in the region until the end of the year, with troops having failed to wrest back the southern city of Marawi following two months of fighting.
The military said only about 60 Islamic State group- inspired gunmen are left in a 49-hectare (121-acre) area of Marawi, but Duterte said he needed martial law powers to rebuild the city and ensure the war did not spread elsewhere.
"If there is a spillage it will not be as bad if you have this stopgap," he added.
Duterte imposed a 60-day martial rule -- the maximum period allowed by the constitution -- over the Mindanao region on May 23 within hours of the gunmen beginning their rampage.
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On Monday he asked Congress to extend it until the end of the year, along with the continued suspension of a constitutional safeguard against warrantless arrests.
A slide presentation accompanying Duterte's request, seen by AFP, compared the Marawi crisis to the IS takeover of the Iraqi city of Mosul.
Marawi itself could now become a magnet for foreign fighters in Iraq and Syria, it added.
Martial law allows the military to establish control with measures such as curfews, checkpoints and gun controls in a country where civilians are authorised to keep licensed firearms in their homes.
However, any martial law extension must be approved by Congress.
The subject remains sensitive in the Philippines decades after the late deposed dictator Ferdinand Marcos put the country under military rule for part of his 20-year term.
"I am amenable to it," House of Representatives justice committee chairman Reynaldo Umali, a key Duterte ally, told ABS-CBN television yesterday.
House Speaker Pantaleon Alvarez has said previously he sees no roadblock to its swift approval by both chambers of Congress.
Duterte had already beaten back a Supreme Court petition to declare martial law in Mindanao illegal.
But opposition politicians have criticised Duterte's proposal for a martial law extension, with some alleging it is part of a Duterte plot to eventually bring the country under a military-backed dictatorship.
After this he could declare a revolutionary government to allow him to stay in office beyond his six-year electoral term in mid-2022, Trillanes says.
Duterte, 72, insists he has no plan to stay in office beyond his term.