The Philippines on Friday placed 42 airports on “heightened alert” following a bomb threat, its civil aviation authority said.

The Air Traffic Service received a warning via email that bombs could be set off in airplanes from Manila bound for the tourism hubs of Puerto Princesa, Cebu, Bicol, and Davao, the aviation authority said in a statement. 

“While the information is currently under validation, immediate enhanced security measures are being implemented across all airports,” it said.

The agency said it’s working with the police and military to intensify monitoring and intelligence gathering. Security at the airports have also been tightened with stringent access control procedures for both personnel and vehicles and thorough inspections of passengers and cargo, it said.

“There are no expected impact to any scheduled flights and we would like to assure the traveling public that protocols are in place to ensure everyone’s safety and security,” Transportation Secretary Jaime Bautista said in a separate statement.

On Oct. 2, a bomb joke disrupted flights at the Bicol International Airport, ABS-CBN News reported.