Flights from Sharm el-Sheikh to the UK were suspended tonight amid fears that a Russian plane was brought down by a bomb, Downing Street has announced.
The "precautionary" move is to allow time for a specialist British team to assess security arrangements in the Egyptian resort.
A Number 10 spokeswoman said: "While the investigation is still ongoing we cannot say categorically why the Russian jet crashed. But as more information has come to light we have become concerned that the plane may well have been brought down by an explosive device.
"In light of this, and as a precautionary measure, we have decided that flights due to leave Sharm for the UK this evening will be delayed.
"That will allow time for a team of UK aviation experts, currently travelling to Sharm, to make an assessment of the security arrangements in place at the airport and to identify whether any further action is required. We expect this assessment to be completed tonight."
It is believed that up to 20,000 Britons are in the Sharm area.
Prime Minister David Cameron will chair a meeting of the Cobra emergency committee on the issue later.
All 224 people on board were killed when the Metrojet flight bound for St Petersburg from Sharm came down in the Sinai desert on Saturday.
The nature of the crash and the lack of an SOS call have fuelled speculation that it was caused by a bomb or missile.
The Prime Minister spoke to Egyptian president Abdel Fatah al-Sisi last night to discuss security measures at the popular holiday resort's airport.
The Number 10 spokeswoman said there were no more departures from the UK to Sharm el-Sheikh due today.
"We would underline that this is a precautionary step and we are working closely with the airlines on this approach," she added.
"We recognise that this information may cause concern for those in Sharm and indeed for those planning to travel to Sharm in the coming days.
"We have deployed extra consular staff to Sharm who will be on hand at the airport, working with the airlines, to assist British holidaymakers there. For others, either in resorts at Sharm or planning a holiday to Sharm in the coming days, our advice is to contact your airline or tour operator.
"At this stage we are not changing the level of our travel advice."
A Thomson flight to Manchester was scheduled to take off at 6.35pm local time, according to Sharm el-Sheikh Airport's website, and an easyJet flight was due to leave for Luton at 6.45pm, with another to London Gatwick at 7.05pm.
Transport Secretary Patrick McLoughlin said: "There have been already people sent out from the United Kingdom today to review the security arrangements at the airport.
"That is taking place. It is when that review is completed that we will allow the flights that are there tonight to depart."