Blunt plays the magical nanny, taking over the role from Julie Andrews, while Dick Van Dyke also makes an appearance in the footage, 54 years after he starred in the first Mary Poppins film.
He plays the son of Mr Dawes, the banker he played in the original movie, while Ben Whishaw and Emily Mortimer play the grown-up incarnations of Michael and Jane Banks.
The clip also gives a look at Lin-Manuel Miranda as a dancing lamp lighter, as well as glimpses of Meryl Streep, Colin Firth, Dame Julie Walters and Angela Lansbury.
In the footage Poppins returns to visit the Banks children as they are struggling to hold on to their house on Cherry Tree Lane, and Michael is trying to care for his children after the death of his wife.
There is also an animated sequence in the style of the original film that features a dance number and magical animals.
The trailer ends with Blunt saying “Off we go” before falling backwards into a bubble bath.
Mary Poppins Returns is released in the UK on December 21.