The first flights have resumed at Gatwick airport after a series of drone sightings caused days of disruption, affecting more than 100,000 passengers.

Airlines warned customers to continue to check their flight’s status on Friday morning as the airport worked to “introduce a limited number of flights over the coming hours”.

The runway had remained closed throughout Thursday night, forcing passengers to search for accommodation or shelter at the airport, and bringing demands for new aviation regulations to tackle the threat.

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The airport’s chief operating officer, Chris Woodroofe, said 120,000 passengers’ flights had been disrupted by the incident.

On Thursday night police said there had been more than 50 sightings of the drone in 24 hours from when the runway was first closed. Night-flight restrictions had been lifted at other airports, so “more planes could get into and out of the country”, the transport secretary, Chris Grayling said.

“This is clearly a very serious ongoing incident in which substantial drones have been used to bring about the temporary closure of a major international airport,” he said.

“The people who were involved should face the maximum possible custodial sentence for the damage they have done. The government is doing everything it can to support Sussex police.”

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Shooting down the drone was being considered as a “tactical option” after other strategies to stop it had failed.

Amid disbelief that the drone incident could be enough to bring one of the UK’s key airports to a standstill, the perpetrator or perpetrators eluded a search conducted by 20 units from two police forces in the surrounding area. Meanwhile, an emergency Whitehall meeting was called to decide on a response to the ongoing crisis and the airport warned that the disruption could mean further cancellations on Friday.

At least two drones, described as “substantial” by the government, “commercial” by the transport secretary, and “industrial” by police, were spotted repeatedly by staff in and around the airport perimeter from Wednesday night.

Sussex police said they believed the incident was a deliberate attempt to disrupt the airport’s operations, but unlikely to be terror-related. However, despite increasingly urgent demands for information on the circumstances of the incident, the location, motive or identity of the drones’ operators remained unknown.

Det Ch Supt Jason Tingley from Sussex police said: “We don’t know what the drone specification is. Our working assumption is it’s larger than what someone might buy online, we think it may have been adapted and developed. We’re working through CCTV footage and trying to identify the make and model.”

With any airborne collision posing a serious risk to the safety of an aircraft, the police’s search for the operators became increasingly urgent. But Gatwick’s policing commander, Justin Burtenshaw, told the BBC it was a painstaking process because the bigger the drone the further away the operator could be. “Each time we believe we get close to the operator, the drone disappears,” he said.

Aviation bodies and politicians demanded tougher laws on drone use as the vulnerability of Britain’s second biggest airport became apparent.

Facebook Twitter Pinterest A police helicopter flies over Gatwick airport as the airport remains closed. Photograph: Tim Ireland/AP

About 800 flights have been cancelled so far since the first reports of drones at 9.03pm on Wednesday. The runway briefly reopened at 3.01am on Thursday morning but closed 45 minutes later after a further drone sighting.

Some passengers reported being stuck on the tarmac for hours, while inbound flights were diverted to alternative airports as far away as Amsterdam and Paris.

As the time of the airport’s reopening crept later and later and the number of flights cancelled continued to soar, Gatwick condemned an act that it said was designed to cause “maximum disruption in the run-up to Christmas”. It was not clear by evening when normal service would resume. Ryanair said all its scheduled services to and from Gatwick on Friday would operate from Stansted.

The transport secretary, Chris Grayling, who ordered night flying restrictions to be lifted across other airports “so that more planes can get into and out of the country”, said that the perpetrators should face a heavy custodial sentence.

No group has claimed responsibility. Climate protesters including Extinction Rebellion, which have been engaged in direct action to highlight climate change, denied involvement.

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EasyJet, which operates almost half of all flights at the Sussex airport, announced at 5pm that it was cancelling all remaining flights on Thursday. It warned passengers not to travel to Gatwick on Friday until checking the status of the flight, adding: “At this stage there is no indication of when the airport might re-open ... We expect disruption to continue into tomorrow.”

Some customers have been rebooked on flights from other airports, while others were put up in hotels. However, many thousands remained at the airport terminals waiting for information as the reopening was repeatedly postponed by hours throughout the morning and early afternoon.

The uncertainty resulted in many having a fruitless wait at Gatwick. Zak Morgan, 20, a computer science student at UCL, boarded a flight to Paris on 8.45pm on Wednesday, but passengers were disembarked after several hours waiting on the tarmac. His journey was rescheduled, via Barcelona, departing at 3pm on Thursday, but cancelled again. “Every hour they have been changing the flight times, so instead of saying go home, they’ve been telling us to stay,” Morgan said.

Another passenger, Mamosta Abdulla, was due to fly to Iraq on Wednesday evening before getting stuck on the plane waiting to take off for four hours. Passengers were given a voucher for food, he said, but were left to sleep “in a freezing place on uncomfortable chairs”. He added: “We are in Iraq with bombs going off nearby and the plane still lands. But here some drones have shut down the airport.”

The incident highlighted the authorities’ inability to stop illegal drones flying. Police said shooting down the drone might be possible. Tingley said: “One of the options is to use firearms officers if that presents itself – they have been out on the ground today and that’s a consideration … There are a number of factors in terms of range, the height of the drone and the likely impact on us firing at the drone but that is a tactical option.” The defence secretary, Gavin Williamson, said that the military was offering assistance, but did not specify how.

The pilots union Balpa, which has been campaigning for tougher laws after an increasing number of near misses between drones and commercial aircraft, called to extend the 1km drone exclusion zone around airports – introduced this year – to 5km (3 miles). Brian Strutton, general secretary, said: “It is now obvious that that must happen urgently. This incident also reinforces the need for registration and licensing of operators so that the police can track and trace drones.”

Facebook Twitter Pinterest An information board shows scheduled flights arrivals cancelled and diverted at Gatwick airport. Photograph: Glyn Kirk/AFP/Getty Images

Liz Sugg, the aviation minister, told the Lords that new laws would mean from November 2019 new purchases would be registered and operators would have to take an online safety test.

But the Liberal Democrat transport spokeswoman, Jenny Randerson, said the incident at Gatwick “illustrated the frightening ease with which drone vessels can inflict massive damage to our safety, our security and our economy”.

The shadow transport secretary, Andy McDonald, said the government had “been too slow to act”, and called on ministers to fast-track rules to ensure the safety of airspace.

According to the Civil Aviation Authority, airlines will not be obliged to pay financial compensation to those hit by the disruption at Gatwick because it is an “extraordinary circumstance”.

Despite the chaos for passengers ahead of Christmas, some observers saw an upside to the day’s events. Sally Pavey, of local campaign group Cagne – Communities Against Gatwick Noise and Emissions – said she had sympathy for stranded passengers and did “not condone people doing such irresponsible acts”. But she added: “The tranquillity was delightful to enjoy. People were able to sleep last night because there weren’t aircraft booming off over their head.”

• The graphic in this article was amended on 21 December 2018 because an earlier version said drones must not fly within 50 metres of crowds and built up areas. This has been corrected to say 150 metres.