import re

text = """2018-01-09 04:50:25,226 [18] INFO messages starts here line1
line2 above error continued in next line
2018-01-09 04:50:29,226 [18] ERROR messages starts here line1
line2 above error continued in next line
2018-01-09 05:50:29,226 [18] ERROR messages starts here line1
line2 above error continued in next line"""

matches = re.findall(r'(\d{4}(?:-\d{2}){2}\s\d{2}(?::\d{2}){2})(,\d+[^\]]+\])\s(INFO|ERROR)\s([\S\s]+?)(?=\r?\n\d{4}(?:-\d{2}){2}|$)', text)

print(matches)