British police say two people were arrested early on Saturday morning for suspected 'criminal use of drones'' in the Gatwick Airport case that has created nightmarish holiday travel delays for tens of thousands of passengers.

Sussex police did not release the age or gender of the two suspects arrested late on Friday night and did not say where the arrests were made. The two have not been charged.

Police superintendent James Collis asked the public in the Gatwick area to remain vigilant. 'Our investigations are still ongoing, and our activities at the airport continue to build resilience to detect and mitigate further incursions from drones by deploying a range of tactics,' he said.

New drone sightings on Friday had caused fresh problems for holiday travelers at the airport, which reopened in the morning after a 36-hour shutdown only to hastily suspend flights for more than an hour in the late afternoon on one of the busiest travel days of the year.

Passengers wait at Gatwick airport on Friday. AP

The reopening, closing and re-reopening of Britain's second-busiest airport due to repeated drone sightings raised a host of questions for British officials, including questions about how safe it really is to fly with drones around and why it took so long to make arrests.

The Friday night flight suspension at Gatwick caused still more delays and cancellations just as the holiday travel season peaked. The persistent drone crisis at Gatwick, located 45 km south of London, has had ripple effects throughout the international air travel system.

The latest drone sighting came after British police and transport officials said extra measures had been put in place to prevent drones from intruding on the airport, which serves 43 million passengers a year.

Military forces with special equipment have been brought in and police units are working around-the-clock. Police say a sophisticated drone operation is targeting the airport to cause maximum disruption during the holiday rush.

The motive for the drone invasion wasn't clear but British police said there are no indications it was 'terror related'.

Gatwick reopened at about 6 am on Friday after having been shut down on Wednesday night and all day Thursday after authorities said drones repeatedly violated the airport perimeter, threatening the safely of incoming and outgoing planes.