A British nurse was on Friday found guilty of murdering seven newborn babies and trying to murder six others at the hospital neonatal unit where she worked with sick and premature infants.

Lucy Letby, 33, who has been on trial since last October, was accused of injecting her young victims with air, overfeeding them milk and poisoning them with insulin.

The jury at Manchester Crown Court in northern England reached its verdicts after deliberating for 22 days.

Letby was arrested following a string of baby deaths at the neonatal unit of the Countess of Chester Hospital in northwest England between June 2015 and June 2016. 

Described by the prosecution as a "calculating" woman who used methods of killing that "didn't leave much of a trace", Letby had repeatedly denied harming the children.

The court heard that colleagues raised concerns after noticing that Letby was on shift when each of the babies collapsed, with some of the newborns attacked just as their parents left their cotsides.

Prosecutor Nick Johnson said Letby "gaslighted" her colleagues into believing the string of deaths were "just a run of bad luck".

Letby's final victims were two triplet boys, referred to in court as babies O and P.

Child O died after Letby's return from a holiday in Ibiza in June 2016 while child P died a day after their sibling.

Letby was also said to have attempted to kill the third triplet, child Q, but the jury was unable to reach a verdict on the charge.