Duterte, who ran Davao for more than two decades as its crime-busting mayor, said the explosion late on Friday outside a high-end hotel intensified what was an "extraordinary time" in the Philippines, and police and military would redouble efforts to crush crime, drugs and insurgency.
Deadly Philippine bomb attack 'terrorism': Duterte
"I must declare a state of lawless violence in this country, it's not martial law," Duterte told reporters on a Davao street at daybreak.
"It's not martial law until it's a threat against the people and against the nation ... I have this duty to protect this country."
There was no immediate claim of responsibility for the explosion, which police said killed 14 people and wounded 67. They did not reveal any findings from their initial investigation.
Duterte was not near the scene of the blast when it happened.
It comes as the uncompromising president wages war with just about anyone from drugs kingpins and street dealers to Islamist rebels and corrupt bureaucrats, scoring big points in opinion polls, but at a risk of making powerful enemies.
It was not immediately clear what a "state of lawlessness" entailed.
Duterte's office said it "was rooted" in an article of the constitution that puts the president in charge of all armed forces and states that when necessary, he "may call out such armed forces to prevent or suppress lawless violence, invasion or rebellion".
DEATH THREATS
Rumors have swirled in recent days of a plot to assassinate Duterte, 71, which he has shrugged off as part of his job. The talk has been intensified by a crackdown on drugs that has killed more than 2,000 people since his June 30 inauguration.
Explosion in Philippine president's home city kills 10
Asked on Thursday about death threats, his spokesman, Ernesto Abella said: "He eats that for breakfast, it's not something new."
The explosion went off at about 10.30 p.m. at a night market outside the Marco Polo hotel, a place Duterte visits often and used for meetings during his national election campaign. He typically spends his weekends in Davao.
Asked if he thought the blast was the work of drugs gangs, Duterte said: "It is also being considered ... At least we know who made the threats."
The White House expressed condolences to the families of victims and offered assistance, which National Security Council spokesman Ned Price said President Barack Obama would convey when he meets Duterte at a summit in Laos next week.
Duterte's Communications Secretary Martin Andanar said the president would forge ahead with what would be his first overseas trips, although he was initially reluctant.
Don't do drugs: Philippine's Duterte to workers returning from Saudi
He was due to visit Brunei and Indonesia before going to an Association of South East Asian Nations (ASEAN) and East Asia Summits in Laos starting on Tuesday.
Though Davao itself is relatively safe, it is in Mindanao, a large southern island province beset by poverty and decades of Muslim insurgency.
Operating in the jungles of some of its smaller islands is the Abu Sayyaf, a rebel group loosely linked to Islamic State and notorious for kidnappings, which Duterte has promised to flush out with stepped-up military offensives.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ