The widow of a New York police officer shot dead in an ambush has given birth to his child more than two years later.

Pei Xia Chen became pregnant through IVF using sperm preserved from her husband Wenjian Liu.

The detective, 32, was killed along with partner Rafael Ramos, 40, as they sat in a patrol car in Brooklyn in December 2014.

On the night of his death Ms Chen requested that her husband's sperm be frozen.

Rafael Ramos and Wenjian Liu, right, were shot dead while sitting in their patrol car in Brooklyn (EPA)

She welcomed the couple's baby daughter Angelina into the world on Tuesday at Weill Cornell Hospital, where she was joined by her husband's parents.

The girl was named in tribute to her slain father.

“Her name is Angelina, like an angel, like my son is an angel,” Mr Liu’s mother Xiu Yan Li told the New York Daily News.

“I'm just so happy," she added.

Ms Chen and Mr Liu were married for just three months before the officers were killed by Ismaaiyl Abdula Brinsley, who later shot himself dead.

Brinsley had earlier posted social media rants about alleged abuse of black Americans by US police forces.

Mr Liu had hoped to have a child with his wife before his life was cut short.

His widow said that on the day she underwent the IVF procedure she dreamed about her husband handing her a baby girl.

She added: “I told my friend, ‘It’s going to be a girl.' My friend said, ‘No, you haven’t even checked the sonograms.’ But I was right."