The AIB IHS Markit Purchasing Managers' Index (PMI) inched down to 63.4 from 63.7 last month and from a two-decade peak of 66.6 in July. A reading above 50 indicates an overall increase in activity compared to the previous month.

AIB chief economist Oliver Mangan said the sector continued to experience "robust expansion", with readings over 60 registered for six months in a row as the near-complete easing of COVID-19 restrictions releases pent-up demand.

The survey showed the rate of growth in outstanding business reached its highest level in 21 years after eight months of expansion.

Both input price inflation and prices charged were at their highest rates since 2000, the survey showed.

(Reporting by Conor Humphries; Editing by Catherine Evans)