The search for a missing Irish climber on Mount Everest is now a recovery operation, according to the trekking company which organised the trip.
Mingma Sherpa, owner of Seven Summits Treks, said conditions descending the mountain were "very good" but that Mr Lawless appears to have had an accidental fall.
"The Sherpas were shouting for him last night but couldn't find him."
There were further searches once Mr Lawless' GPS coordinates were established, however he has not been located.
The GPS worn by Mr Lawless was found almost 500 metres from where he fell, however experts say it is possible that the device became detached from Mr Lawless.
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The climbing group has not yet returned to Everest base camp so the exact details of the incident are still unclear and poor weather means searches will not resume for a number of days.
Winds of up to 100kph are being experienced on Everest and the temperature is dropping as low as -45C.
"It is a very difficult situation. We are searching for a body," Mr Sherpa said.
Mr Mingma confirmed he has spoken to Mr Lawless's wife.
"She called me many times, but how do we explain the details? When the team returns we will have more details."
"We are very sad because we have lost one of our best mountaineers. Everybody is very upset in the Himalayas."
Mr Lawless was taking part in the expedition to raise funds for the Barretstown children's charity.
Professor Vinny Wade of Trinity College issued a statement this evening saying: "At this deeply upsetting time, we are thinking of our friend and colleague, Séamus (Shay) Lawless.
"On behalf of everyone at ADAPT and Trinity College Dublin, we are offering our support to his wife, Pam, and their daughter, Emma, and to all his family and friends.
"Shay is an Assistant Professor and Principal Investigator at ADAPT and one of our research leaders, an inspirational colleague, and a much loved and valued member of our family.
"His decision to climb Mount Everest to support the Barretstown Children's Charity exemplifies all the things we love about Shay: his boundless enthusiasm, his courage, and his determination to help and inspire others.
"We are extremely distressed at what has happened on Mount Everest and we hope that he is found safely as soon as possible."
A mountaineer who has twice reached the summit of Mount Everest has said his thoughts are with Mr Lawless's family and friends.
Speaking on RTÉ's Morning Ireland, Pat Falvey said the area that Mr Lawless was last seen is one of the most amazing places on Earth, but that it is also very steep.
He said that as long as Mount Everest is the highest mountain in the world, then people will attempt to climb it.
Almost 300 climbers have lost their lives on Mount Everest over the years.
"Everybody that goes there is very much prepared, but of course there's risk, it's one of the things that goes with it. At this stage, it's a matter of waiting and hoping, and hopefully things will turn out well but as the day progresses things will become more clear."
Mr Falvey said he spoke to Mr Lawless a few weeks ago, and that he was very excited about the climb.
He said it was fantastic that he reached the summit, but said that is only half the journey.