A Lower Hutt bus driver is believed to have collapsed and died after chasing a youth he spotted stealing the cash box from his bus, police have told his family and friends.

At a funeral service on Sunday night, a Lower Hutt detective said 64-year-old Herman Curry stopped near the entrance gates of the Waterloo Interchange Bus Depot during the chase and clutched his side, according to one of the alleged thieves.

Curry then turned around and walked back into the depot, the detective said.

A colleague found him about 10pm on Friday, April 27, on the ground next to his bus with blood on his face.

Preliminary findings from a pathologist suggest he died of natural causes, most likely a heart attack, the Dominion Post reports.

Two men, aged 17 and 20, have been charged with theft in relation to the incident, while two others, aged 15 and 16, have been referred to Youth Aid.

All four handed themselves in to police.

A second funeral service was held for the bus driver on Monday.