Kawhia man Trevor Smith had already suffered a heart attack and collapsed down a bank at the Waikato River by the time police acted on his missing person's report, a Coroner has ruled.

An inquest into the death of 70-year-old Trevor looked at the circumstances of the death and how a missing person's report sat idle for 24 hours after his family reported him missing from Waikato Hospital on March 16, Fairfax reports.

Trevor Smith died of a heart attack a day after his family reported him missing.

Police told Coroner Gordon Matenga the officer involved has since had extra training and procedures have been changed so this sort of thing doesn't happen again.

An investigation was launched on March 17, with search and rescue teams working alongside family members as they searched for Trevor, who had dementia.

CCTV footage showed Trevor near Pak ‘n' Save on Clarence Street.

Police search and rescue teams continued to search for the 70-year-old for three weeks until his body was found by four teenagers on a steep bank near the Waikato River on April 6.

After visiting the site where Trevor was found and further investigations into his death, Coroner Gordon Matenga ruled Trevor died from a heart attack on March 17.