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)

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