At least 12 people were killed, and dozens more were wounded in an explosion that hit a market place in Davao city in the southern Philippines on Friday.
The cause of the blast is not immediately clear, and there is no claim of responsibility.
Regional police chief Manuel Guerlain said a ring of checkpoints had been thrown around the city's exit points.
"A thorough investigation is being conducted to determine the cause of the explosion," he said.
"We call on all the people to be vigilant at all times."
Davao City is located in Mindanao, a large southern island beset by decades of insurgency. The region is also home to Abu Sayyaf, an Al Qaeda-linked militant group that is notorious for making millions of dollars from kidnappings.
The city, which is President Rodrigo Duterte’s hometown, was largely peaceful in recent months.
The president has been credited with transforming Davao from a lawless town to a southern commercial hub for call centres and offshore business processing services.
At the time of incident, he was in Davao, but he is not hurt as he was nowhere near the scene of the blast.