An 11-month-old boy has died in hospital, a day after being critically injured in a car crash in Sydney’s southwest.

Police are investigating whether the baby was properly restrained when the BMW he was in collided with a Mercedes-Benz at Lurnea on Monday evening.

The collision triggered the BMW driver’s airbag, inflicting critical head and facial injuries on the baby.

He was airlifted to The Children’s Hospital at Westmead but died late on Tuesday.