It should be considered a medical emergency (regardless of whether there is pain) and medical attention should be sought immediately, as if it is left untreated it can lead to death of the mother and/or fetus.
^Lam CM, Wong SF, Chow KM, Ho LC (2000). "Women with placenta praevia and antepartum haemorrhage have a worse outcome than those who do not bleed before delivery". Journal of obstetrics and gynaecology : the journal of the Institute of Obstetrics and Gynaecology20 (1): 27–31. doi:10.1080/01443610063417. PMID15512459.