The 89-year-old man was hit by a blue Vauxhall Astra in Boston Street nesr the junction with Cemetery Road just after 12pm today (Sun Jan 15).
He suffered life-threatening injuries and was taken to hospital.
A 40-year-old man has been arrested on suspicion of being over the prescribed limit and being unfit to drive through drugs. He remains in custody being questioned by officers.
Any witnesses are asked to call police on 101 or email [email protected] quoting incident number 437 of 15 January 2017.