Filipino survivors and their families on Wednesday held a prayer vigil to mark the 25th anniversary of a massive volcanic eruption that leveled the northern Philippines.

The Mount Pinatubo eruption in June 1991 was the second largest volcanic eruption in the 20th century, with over 5 billion cubic meters of ash released and reaching 34 kilometers (21 miles) high in the atmosphere.

Villagers in Pampanga province chanted prayers along a highway and visited sites that were buried under twenty feet of lahar or hardened ash.

A special Catholic service was held at San Guillermo church, one of the surviving structures that was half-submerged in lahar.

"We thought it was the end of the world. What we can only do was pray because we cannot leave our homes since the ash from Mount Pinatubo was so thick," said Cel Mariano, a church staff and one of the survivors of the eruption.

Evelyn Puno, a 16 year old student, being taught about the disaster was a lesson for what may happen in the future.

"No matter how strong the calamity is, as long as we're ready, we can surpass it," she said.

The Office of the Civil Defense reported only 847 casualties, but the eruption displaced more 250,000 families and changed the landscape of northern Philippines.

The local government has relocated affected families to other parts of Pampanga, constructing large dikes and rebuilding homes on top of the old ones.

A museum was also recently opened to facilitate guests and the youth who wanted to learn more about the eruption.

"They have no recollection of it, they were not even born that time, and those who were there to experience it, have forgotten about it. So we felt that it is our duty to remind them and to make sure that they don't forget what happened then," said Robby Tantinco, director for the Center For Kapangpangan Studies.

Mount Pinatubo's eruption affected the world, with global temperatures dropping by 0.5 degrees Celsius for two years after millions of tonnes of sulfur dioxide blocked the sunlight and cooled the earth, scientists said.

The Pampanga local government has declared June 15 a holiday in the province as part of the anniversary commemoration.