Pampanga (CNN Philippines, April 24) — Officials of the Clark International Airport are launching an investigation into the contractor of its old terminal after a strong quake caused its ceiling to collapse.

Clark International Airport Corporation President Jaime Melo on Wednesday said its legal team has started reviewing the contract of E.M. Cuerpo Incorporated, the contractor of the old passenger terminal building, following allegations the airport was constructed using substandard materials.

"We can get back to the contractor if we find that its substandard... We're checking if its substandard. We're checking the contracts done six years ago," he said.

The 6.1-magnitude earthquake that jolted Luzon on Monday damaged over 1,000 square meters of the old terminal building, which opened in 2013. A part of the ceiling at the check-in lobby collapsed, injuring seven persons. The fire alarm was also affected, causing water leakage from the collapsed building.

Transportation Secretary Arthur Tugade said it will cost P30 to 50 million to repair the damage. For now, the Clark airport management will shoulder the repair cost.

Aside from the infrastructure damage, the Clark airport was paralyzed for nearly 48 hours. The airport's closure left flights canceled and thousands of passengers stranded.

CNN Philippines correspondent Makoi Popioco contributed to this report.