Sum 3d numpy array [i,j] along i elements

Question

For a numpy array of shape([N,N,3]),

[[1,2,3], [1,2,3],[1,2,3]],
[[4,5,6],[4,5,6],[4,5,6]],
[[7,8,9],[7,8,9],[7,8,9]]

How can I get a [N,3] with