Prime Minister David Cameron has said his "thoughts and prayers" are with British nurse Pauline Cafferkey, after doctors revealed today that her condition had worsened.
Cameron sent his message of support to the healthcare worker via Twitter.
My thoughts and prayers are with nurse Pauline Cafferkey who is in a critical condition with Ebola.
Scottish First Minister Nicola Sturgeon has sent a message of support to British nurse Pauline Cafferkey, after doctors revealed her condition had worsened.
Our thoughts continue to be with Pauline Cafferkey and her family during this extremely distressing time.
I would like to thank all of the health professionals involved in treating Pauline, as they continue to show tremendous dedication and expertise
A British nurse diagnosed with Ebola after returning to Glasgow from Sierra Leone is in a critical condition, health chiefs have said.
In a statement, Royal Free Hospital in north London said Pauline Cafferkey's condition had deteriorated and she was now considered critical.
Trained nurse Ms Cafferkey, aged 39 from Glasgow, had agreed to blood plasma treatment and an experimental anti-viral drug, despite a lack of proof that it worked.
In a statement on its website, the hospital said:
[We are] sorry to announce that the condition of Pauline Cafferkey has gradually deteriorated over the past two days and is now critical.
All passengers who were on flights with Scottish nurse Pauline Cafferkey who caught Ebola have been contacted, Public Health England has announced.
#Ebola contact tracing update 1/3: All 101 UK-based passengers & crew on Royal Air Maroc flight AT0800 Casablanca-Heathrow contacted by PHE
2/3 Passengers given advice & reassurance. Additional 31 international passengers being contacted by international public health authorities
3/3 All 71 passengers and all crew members on BA flight BA1478 from Heathrow to Glasgow have been contacted by Health Protection Scotland
The Government's chief medical officer has said Britain's Ebola screening process will be reviewed after an NHS nurse returned from west Africa carrying the deadly virus.
Doctors caring for Pauline Cafferkey said she has agreed to a treatment that includes an experimental anti-viral drug, despite the lack of proof that it can successfully support Ebola victims.
ITV News Reporter Martha Fairlie reports from London's Royal Free Hospital:
The Royal Free Hospital said the treatment of Pauline Cafferkey is "quite separate" from the treatment of fellow British volunteer nurse William Pooley earlier this year.
"We're starting from the beginning again," Dr Michael Jacobs said. "We're treating Pauline absolutely on her own merits."
Dr Jacobs explained the use of an experimental anti-viral drug as part of the Scottish nurse's specialist treatment in London, despite the fact it is "not proven to work".
At the moment, we don't know what the best treatment strategies are. That's why we're calling them experimental treatments.
As we've explained to Pauline, we can't be as confident as we would like. There's obviously very good reason to believe it's going to help her, otherwise we wouldn't be using it at all, but we simply don't have enough information to that's the case.
The one thing I'll say about the drug - it has been used extensively in people previously for different reasons, and it has a very good safety record in humans which has encouraged us to use it in this experimental way.
Dr Jacobs said doctors were taking Ms Cafferkey's treatment "day by day" and would get a "clearer picture" about the impact of their decisions in "a few days' time".
Pauline Cafferkey is "sitting up and talking" with her family while receiving specialist Ebola treatment via a quarantine tent at the Royal Free Hospital, her doctor has said.
Along with receiving an experimental anti-viral drug, Ms Cafferkey is being treated with convalescent plasma taken from the blood of a European patient who has been treated and survived Ebola.
She is sitting up and talking. She is able to read. She's been eating a bit, drinking and she's been in communication with her family, which has been really nice.
She's as well as we can hope for at this stage of the illness. She's had the treatment, it's gone very smoothly, no side-effects at all.
Doctors have said the experimental anti-viral drug being treated to the British nurse who contracted Ebola in Sierra Leone is "not proven to work".
Dr Michael Jacobs said London's Royal Free Hospital was unable to obtain the drug used to treat fellow British volunteer nurse William Pooley, who recovered from Ebola.
Dr Jacobs said ZMapp was not available to Pauline Cafferkey as "there is none in the world at the moment".
"Although it's been used in a handful of patients, we simply don't know if ZMapp works and is of benefit to patients," he said.
Pauline Cafferkey, the nurse who contracted Ebola in Sierra Leone, has agreed to be treated with an experimental anti-viral drug, doctors at London's Royal Free Hospital said today.
British Airways said it is "working closely" with health authorities in England and Wales after a passenger on a flights from Heathrow to London was diagnosed with Ebola.
Customers who flew from London Heathrow to Glasgow on BA1478 which departed at 21.00 on Sunday December 28 and have concerns should contact the special number, 08000 858531, set up by the Scottish Government.
"The safety and security of our customers and crew is always our top priority and the risk to people on board that individual flight is extremely low," BA added.