burst into

1.  Also, burst out in or into. Break out into sudden activity. For example, burst into flames means "break out in a fire," as in This dry woodpile may well burst into flames. A version of this term, which dates from the 16th century, was used figuratively by John Milton: "Fame is the spur ... But the fair guerdon [reward] when we hope to find, and think to burst out into sudden blaze" ( Lycidas, 1637).
2.  Also, burst out. Give sudden utterance to. For example, burst into tears or laughter or song or speech or burst out crying or laughing or singing, etc. mean "begin suddenly to weep, laugh, sing," and so on, as in When she saw him, she burst into tears, or I burst out laughing when I saw their outfits, or When they brought in the cake, we all burst into song. These terms have been so used since the late 1300s.