At least four people were killed and dozens injured in an explosion at a mass Sunday Mass at a university high school in the Philippines.

The explosion occurred in Marawi on the southern island of Mindanao on Sunday morning, according to CNN affiliate CNN Philippines.

Pictures from the scene showed soldiers and emergency workers standing among the debris after the blast at the gymnasium. Part of the seating area was blown away, chairs were scattered across the floor.

Lanao del Sur provincial governor Mamintal Adiong Jr. said there had been a "violent bombing" of a gymnasium at the Mindanao State University during a mass congregation Sunday.

Speaking to reporters at the Amai Pakpak Medical Center, a government hospital in Marawi, Adiong Jr. said more than 40 people were being treated at the center, while a number of others with minor injuries were treated at the university's infirmary.

In a tweet on Sunday, Philippine President Ferdinand Marcos Jr. condemned the attack, describing it as "senseless and most despicable, carried out by foreign terrorists". He did not name any specific group or provide further details.

He added: "Extremists who perpetrate violence against the innocent will always be considered enemies of our society."

The island, the second largest in the Philippines, has long been a hotbed of insurgencies against the Philippine government.

While the Philippines is predominantly Catholic, Mindanao is home to a significant Muslim population.

In 2017, ISIS-linked militants besieged Marawi for five months. The violence forced more than 350.000 residents to flee the city and surrounding areas before the government liberated the city.