According to the Rappler news portal, police have announced that 20 civilians are among those killed in the explosions, while soldiers account for the rest of the victims.
Mujiv Hataman, the governor the Autonomous Region in Muslim Mindanao, where the Sulu province is located, believes that the attack has been most likely committed by terrorists.
"At this point in time, we do not want to make speculations, but we can be sure that this is 99% the handiwork of terrorists," Hataman was quoted as saying by the news portal.
Later in the day, Pope Francis condemned the bombing attack inside the cathedral referring to it as "terrorist attack".
At least five soldiers were among those killed.
According to the police, all the injured people were evacuated immediately.
The country's Armed Forces and National Police are currently working to ensure security in the area.