Armed police are conducting extra-security checks at Schiphol airport in Amsterdam after the authorities received reports of a possible threat. Officers searched every car entering the hub while adding it is likely that flights will be delayed.

There is a strong police presence in and around Schiphol, the fifth busiest airport in Europe in terms of passenger volume, the Dutch media reported, citing the local authorities.

Security threat around #Amsterdam#Schiphol airport, military police search every car, and precence at trainstations pic.twitter.com/IpRBBneXwG — Wim Post (@WMPost) July 30, 2016

The city’s mayor, the National Coordinator for Counterterrorism and Security and as Royal Military Constabulary, reportedly introduced the security measures.

Unknown security threat around #Amsterdam Schiphol airport, military police search every car https://t.co/ODKVj7FhEUpic.twitter.com/nm4TZZvbGR — Roeland Roovers (@r0eland) July 30, 2016

“Like the rest of the Netherlands there is extra vigilance at Schiphol. This also applies to other European airports. Additional measures are needed in some cases,” a spokesman for the Royal Military Police told Amstel Television 5.

Ziet er allemaal best heftig uit #schiphol. pic.twitter.com/j76c32Jbuj — Leo Kuyt (@leokuyt_70) July 30, 2016

It’s not yet clear what kind of threat the authorities received and what exactly the police are searching for.

The Algemeen Dagblad newspaper said that passengers have been also subjected to additional checks.

Aangekomen op #Schiphol vanuit Maleisie. Ook hier extra controle zo lijkt het, iedereen wordt tegengehouden. pic.twitter.com/WT2OYJ2kdV — Anouschka Moerel (@AnouschkaM) July 30, 2016

Photos on social media showed long lines of passengers standing in and near the airport. A number of armed police officers could also be seen checking vehicles.