Portugal was Thursday mounting one of its largest- ever security operations ahead of this weekend's NATO summit, with restrictions on air traffic plus nearly 10,000 police officers due to be deployed in Lisbon, DPA reported.
The number of flights coming into Lisbon will be reduced from a maximum of 23 flights per hour to a maximum of 14 flights per hour between Thursday midday and Sunday midday, the air traffic authorities announced.
Around 100 flights will thus be cancelled or delayed, reports said. The authorities said some flights could be diverted to Porto in the north or Faro in the south.
Departing flights were not expected to be affected.
Portugal has also stepped up controls at border posts, lifting the right to free movement within the European Union's Schengen area.
Dozens of people were barred entry into the country, usually for violating immigration regulations. More than 10 people were detained at border posts on Wednesday on charges ranging from drug trafficking to carrying knives.
Portugal was reportedly trying to prevent the kind of violent protests that had erupted during the previous NATO summit in Strasbourg in 2009.
Large numbers of police were patrolling the Lisbon neighbourhood where the summit was due to take place.
Portugal is deploying nearly 10,000 police to guarantee security during the summit, which was expected to bring together at least 22 heads of state, 19 prime ministers and dozens of foreign and defence ministers on Friday and Saturday.