At least 10 people died and 60 were injured when a blast rocked a market area in southern Philippines' biggest city of Davao, authorities said.
The explosion occurred just before 11:00 pm (1500 GMT) close to one of the city's top hotels.
The vice mayor has confirmed there were at least 10 people dead and has asked residents to stay indoors.
Islamic militants and communist rebels have allegedly carried out the attack. The authorities have however stressed that it's too early to determine the cause.
“There was an explosion but, as to what caused it, it is still under investigation," city spokeswoman Catherine dela Rey said.
"Right now, we cannot yet give definite answer to questions as to who is behind this as we are also trying to determine what really exploded," the president's son and Davao vice mayor, Paolo Duterte, said in a statement.
The Communist Party of the Philippines since 1968 has waged an armed struggle, fighting Asia's longest-running Muslim insurgencies that has claimed more than 120,000 lives. The communist rebels maintain a considerable presence in rural areas surrounding Davao.
President Rodrigo Duterte has been widely praised for bringing peace to the city with his stringent security policies.
Duterte has in recent weeks pursued peace talks with the two main Muslim rebel groups. Its leaders have said they want to broker a lasting peace.
Duterte has also ordered an offensive against Abu Sayyaf -- a rebel group that has declared allegiance to the Islamic State and has vowed to keep on fighting.
(WION with input from agencies)