Justin Bieber and Hailey Baldwin were spotted heading into a New York City courthouse today where marriage licenses are issued ... and Hailey was wearing white!

The young couple swore they wouldn't tie the knot until next year, but it looks like they may have had a change of heart.

An eyewitness says he heard Justin crying at one point and said to his fiancee, "I can't wait to marry you, baby," according to TMZ.

Another source told the web site he overheard Bieber telling a courthouse employee: "Thanks for keeping it on the DL." Yet another person says the guy issuing the license was a judge, which means JUSTIN BIEBER AND HAILEY BALDWIN COULD BE LEGALLY MARRIED RIGHT NOW!!!

And here's the last tidbit of "proof" that these lovebirds may have just gotten hitched ... a source tells TMZ he overheard Justin and Hailey saying they were leaving the country. #RomanticHoneymoon??!!