I have following output from script

host1:101 host1:102 host2:101 host2:102 host2:103 host4:101 host5:101 host5:102 host5:103 host5:104 

etc..

I wanted to insert a new line after each host group.

host1:101 host1:102 host2:101 host2:102 host3:101 host3:102 

Any AWK onliners to compare each consecute line with 1st field and insert new line before non-matching 1st field?