IS that correct sentence?

Hi, I saw the the below sentence in a book;
…I must go see her at once…
I would like to know is that correct?

Can I use " I must go to see her at once…?

Yes, with the same meaning. You can also use ‘and’.

Hi, Bee Thanks!

Shouldn’t the sentence have been written with “to see” and not “see” only.

I must go to see her at once.

Thanks

Not necessarily, no. It is correct both with and without ‘to’.