From Longman Dictionary of Contemporary Englishclose in phrasal verb1 NEARto move closer to someone or something, especially in order to attack them The snake closed in for the kill. on/around/upon etc enemy soldiers closing in on them from all sides2 BECOMEif the night, bad weather etc closes in, it becomes darker or gets worse The sun had set and dusk was closing in.3 DNif the days close in, they become shorter because it is autumn → close→ See Verb table
Examples from the Corpus
close on/around/upon etc• Apple is also closing in on completing Rhapsody, aimed mostly at corporate users.• And then Georg had closed in on her, a grumpier, more disapproving, hectoring Georg.• But I suspect McVeigh quickly felt the walls closing in on him from these four sides as the trial progressed.• Hutt crept silently into the kitchen, his hands sweating profusely as he closed in on his prey.• The three space directions and imaginary time would form a space-time that was closed in on itself, without boundaries or edges.• They closed in on the bad.• Smitty went first, forcing his way through the branches that closed in on the trail.• Mayock was closing in on third place as El Guerrouj won in 7min 37.74sec. 