The 91-item Environment in Asia Scan Tool—Hong Kong (EAST-HK) was developed to objectively assess aspects of the neighbourhood environment hypothesised to affect walking in Hong Kong and similar ultra-dense Asian metropolises. Reliability was assessed by four pairs of raters auditing 422 street segments, 204 on two occasions. Seventy-one items showed sufficient variability and reliability. These can be used to estimate neighbourhood walkability in Hong Kong. Fourteen items showed good reliability but limited variability and may be used in a more variable context. Auditing of only 50% of street segments may be sufficient to obtain representative estimates of neighbourhood walkability.