Convicted UK child killer Lucy Letby went on trial again on Wednesday, accused of attempting to murder a baby girl at the hospital neo-natal unit where she worked.

Letby, 34, is alleged to have tried to kill the premature newborn, who was referred to in court as Baby K, at the Countess of Chester Hospital in northwest England in February 2016.

Opening the case, prosecutor Nick Johnson alleged that the former nurse was "caught virtually red-handed" by a senior consultant as she displaced the tiny infant's breathing tube.

"The designated nurse had left (Child K) connected to a ventilator that was breathing for her, and (Child K) was connected to another machine that was checking her heart rate and saturations," he said.

The lawyer explained that alarms would sound if either the baby's heart rate or oxygen saturation levels in the blood fell below a certain level.

But paediatric consultant Ravi Jayaram walked into the nursery and saw Letby standing over the child as her oxygen levels fell, without the alarm going off.

"Not only that, but Lucy Letby was doing nothing," the lawyer alleged.

"We suggest that the fact that Lucy Letby was doing nothing and the fact that the alarms were not sounding is evidence from which you can conclude that it was Lucy Letby, the convicted murderer, who had displaced the tube," he told the jury.

"We say Lucy Letby had been caught virtually red-handed by Dr Jayaram."

The court was told that Letby was convicted at a trial that ended last year of murdering seven babies at the unit and the attempted murders of six more between 2015 and 2016.

Reporting restrictions prevent publication of the identities of the surviving and dead children in the case.

The jury was told that the panel in the first trial could not reach a verdict on the attempted murder charge relating to Baby K, leading to the retrial.

Johnson told the jury that Letby's "status as a multiple murderer and attempted murderer is an important piece of evidence that you should take into account when you are considering whether we have proved that she was trying to kill Baby K".

Letby, who sat in the dock as the prosecutor opened the case, denies one count of attempted murder.

Her lawyer Ben Myers, said: "It's important to emphasise the convictions do not prove this allegation... We say the evidence does not support what has been alleged. It simply does not."