。
Dawn is just starting to break.
Literal
Night [subj-が] open-[half-way-かける]-[toward-speaker-てきた].
~かける ('start to X but not complete') is a different start-auxiliary than ~始める — ~かける implies the action has just begun and is incomplete, often with a sense of being stopped midway. ~てくる adds 'coming (into view)' toward the observer. The combined effect: 'dawn, beginning to appear toward us.'