A Leeds University student, former BBC journalist and two Newcastle United fans are believed to be among the British passengers on board Malaysian Airlines flight MH17.
All 298 passengers and crew died when the Boeing 777-200 crashed in eastern Ukraine after apparently being shot down as it passed over the war-torn country on Thursday.
Tributes on social media have been pouring in for Richard Mayne, a Leeds University student believed to have been on the flight from Amsterdam to Kuala Lumpur.
Friends commenting on Twitter and Facebook said he was a maths and finance undergraduate at the university and had previously studied at The Dixie Grammar School in Market Bosworth.
Writing on Facebook, one friend said: “Words fail me, why do the worst possible things happen to the nicest most kind caring people. Richard Mayne you re an inspiration and will be much loved forever and always xx”
Another wrote: “Richard was a fantastic, friendly, inspirational and very much loved student at The Dixie, words cannot express my sadness.
“The world is missing a very special young man, my thoughts go out to his family and all who will miss him so much.”
Links on Mr Mayne’s profile showed that he had raised more than £1,000 for a children’s charity climbing to the Everest Base Camp in March and was an avid rugby player.
Glenn Thomas, 49, was a media officer at the World Health Organisation (WHO) and was on his way to Australia with a delegation of scientists and activists attending an international Aids conference in Melbourne.
Fadela Chaib, a fellow WHO spokesman said: “I can confirm [Mr Thomas] was on the flight travelling to Australia to attend the Aids conference in Australia.
"For the time being we would like to give his family time to grieve. We have lost a wonderful person and a great professional. Our hearts are broken. We are all in shock."
Mr Thomas, a former BBC journalist, was reportedly from Blackpool and had recently celebrated his birthday.
On Twitter, Timothy O'Leary, a communications team leader at the WHO's Western Pacific office, wrote: "I grieve for my friend and former WHO colleague Glenn Thomas who died in the missile attack on MH17 over Ukraine."
BBC TV news editor Rachel Kennedy wrote: "Horrified to discover lovely Glenn Thomas on MH17. Always a smiling face, will be hugely missed."
Freelance journalist Ilan Moss said: "I'm absolutely devastated to learn of death of WHO colleague Glenn Thomas in MH17 on way to AIDS 2014."
Two Newcastle United fans travelling to see their team play in New Zealand were also feared to be among the victims of the tragedy.
The fans' website NUFC.com reported that John Alder, in his 60s, and Liam Sweeney, 28, planned to watch their team play in a pre-season tour.
A tribute on the website said: "Both were well known to away followers, particularly John, whose usual match day attire led to the affectionate nickname of 'The Undertaker'.
“Both were in attendance at Oldham on Tuesday, doing what they loved. Our thoughts are with their friends, families and the many fans who knew them by sight.
"Watching Newcastle will never be the same again."
There has been no official confirmation that the men were among the British passengers on board.
Malaysia Airlines released a list of passengers’ nationalities immediately after the crash, saying there were nine Britons, 154 Dutch, 27 Australians, 38 Malaysians, 23 US citizens and 80 children were among those on board the flight from Amsterdam to Kuala Lumpur.
Few names have so far been confirmed but Malaysian media released what appears to be a list with details of the 15 Malaysian crew members.
The eight women and seven men were aged between 26 and 53.
Sanjid Singh, an air steward, was only on the doomed jet because he agreed to a rota swap, the Malaysian Insider reported.
The paper said that in a "bizarre twist of fate" Mr Singh's wife, also an air steward, escaped death on flight MH370 131 days ago because she too organised a shift change.
"We are heartbroken because he was our only son. What to do? What has happened, has happened," his father, Jijar Singh, said.