The Philippines have put all their commercial airports on high alert following an anonymous warning that bombs may explode on planes departing from Manila to various destinations, including tourist destinations, the country’s Civil Aviation Authority announced Friday.

“Immediately enhanced security measures” are in place at 42 commercial airports across the country, the Civil Aviation Authority of the Philippines (CAAP) said in a media release, adding that the credibility of the warnings is being verified.

The warning was sent via email to air traffic services and concerned a threat to flights departing from the capital Manila bound for Davao, Bicol and the popular tourist areas of Palawan and Cebu.

“While the information is currently under verification, immediate enhanced security measures are in place at all airports,” CAAP said. The agency did not specify when the warning was sent.

The aviation regulator today released a memorandum dated October 4 instructing airport security officials to step up security measures, to carefully check the luggage and monitor on a 24-hour basis after the warning email.

The October 4 memo included a screenshot of the threat, which did not contain the word “bomb” but said “a plane will explode” today at Manila International Airport and “please be careful.” “Cebu, Palawan, Bicol and Davao will also be affected,” the anonymous email said. A source at Philippines Airlines, who declined to be named, said the carrier is operating as usual. A spokesperson for Cebu Pacific Air said the airline is “following normal protocols.”

Transportation Secretary Jaime Bautista said patrols have been increased and K9 units have been deployed in all terminals at Manila International Airport and that law enforcement agencies are working closely together.

“No impact is expected on scheduled flights and we would like to assure travelers that protocols are in place to ensure everyone’s safety,” Bautista said in a statement.