MANILA — A few seconds of silence, then the first scream of a woman asking for help was heard, followed by crying and panic, as a loud explosion shook the Mindanao State University (MSU), where a Catholic Mass was taking place in Marawi City last Sunday.

People didn't know where to run, some were injured and lying on the ground and asking for help, while others were frozen in fear.

This was seminarian Bro. Remus Tambago's recollection of the moment when an improvised explosive device ripped through MSU's gymnasium.

Bro. Tambago was assisting Father Benigno Flores Jr., who led the morning Catholic service. Tambago said he was at the altar facing the congregation when the bomb exploded about seven to nine meters away.

"After singing the Kyrie and praying the collect of the Mass, before maupo yung mga tao, biglang sumabog. Nakita ko talaga yung pagtilapon ng 2 tao, malayo. Napakalakas ng pagsabog. Suddenly mayroon smoke, yun pala yung mga nasunog na mga victims," he said in an interview in Balo-I, Lanao del Norte.

Tambago said he saw Fr. Flores rooted at where he stood.

"Nakita ko si father medyo nanigas nang kaunti, shocked siya. Ang una ko inisip baka mayroon sa ilalim ng stage, so sabi ko, 'Father, doon tayo sa clear na area, baka mayroon pang kasunod," Tambago said.

Tambago said they spent about 5 to 10 minutes wandering inside the gymnasium before they got out.

He said he saw Evangeline Aromin, who later died, asking for help. He went back inside the gymnasium to assist her and give her holy communion, but she was lifeless when he returned.

"Sabi niya 'Nong, tabangi Nong.' Pero she was so calm. Binalikan ko si Jen, pagbalik ko doon wala na si Jen, patay na. Saka yun si Janine, taga Balabagan, sunog yung katawan niya, putol 2 paa niya,” he said.

Tambago said he felt guilty and angry because he couldn't do anything to help the victims who asked for his assistance.

"Sabi ng commanding officer ng ROTC, yung unang rumesponde, 'Walang gagalaw, kailangan natin ng stretcher.' I feel that na parang ano, guilt, na hindi ako nakatulong saka yung anger. Bakit ganyan, kailangan gawin ito sa payapang nagdarasal?" Tambago said.

Fr. Flores is safe, but he asked for permission to go home to his family in Cebu for stress debriefing, according to Bishop Edwin Dela Peña, the prelate of Marawi.

"Malalim ang trauma, impact. Natulala siya saka hindi niya alam ang gagawin," Dela Peña said.

The bishop said the bomb attack would not stop the Catholic masses in Marawi City and the unity between Christians and Muslims.

"It will not stop us, neither it will not stop us from the partnership, from doing na pagtutulungan na ginagawa namin noon pa hanggang sa ngayon lalo pa ngang umiigting ang aming pagtutulungan," the bishop said.

A small chapel within MSU is being prepared for a Mass on Thursday, the first since in the campus after the explosion.

The Islamic State group has claimed responsibility for the blast.

Military chief General Romeo Brawner earlier said the bombing might have been a revenge attack for government operations against three Islamist militant groups -- Dawlah Islamiyah-Philippines, Abu Sayyaf and Maute -- in western Mindanao in recent days.

Pro-Islamic State Maute and Abu Sayyaf militants -- including foreign and local fighters -- held Marawi under siege in 2017.

The Philippine military wrested back the ruined city after a five-month battle that claimed more than 1,000 lives.

President Ferdinand Marcos Jr. has condemned the attack by "foreign terrorists", describing it as "senseless" and "heinous", while Pope Francis offered his prayers for the victims.