It's becoming morning?
We say "It's getting dark" to mean that the sun is going down and it'll be night soon. How do we say it's becoming morning?
If a few thieves were out to steal something at night how would he warn the others that it's becoming morning?

Question

It's becoming morning?
We say "It's getting dark" to mean that the sun is going down and it'll be night soon. How do we say it's becoming morning? 
If a few thieves were out to steal something at night how would he warn the others that it's becoming morning?

Answer

It's getting light. 
Dawn is coming. 
It's becoming/getting brighter (outside).

several ways to say the same thing

Answer

You could also say "It's almost morning." or "Morning is coming."