He rushed to where the woman was lying on the road and tried talking to her. She blinked twice but was otherwise unresponsive.
Another motorist pulled over and diverted traffic as they waited for police and St John to arrive.
The driver was last night still shaken and was recovering with his family at his Frankton home. He planned to take a couple of days off before returning to work later in the week.
It was the first time he had been in an accident. "Everyone is in shock when something happens like that ... You can't remember. Your mind is shut," he said.
NZ Post group spokesman Richard Trow said Courier Post was carrying out its own investigation and assisting police.
"We are shocked and saddened by the accident." It was rare for one of their vehicles to be involved in a fatal accident, he said.
Waikato road policing manager Inspector Freda Grace said it would be inappropriate to comment about what happened at this stage in the investigation and called for any witnesses to contact police to help them piece together events. "It's very early days. It's just a tragedy really."
She urged road users to take care as the crash brought the Waikato's road toll to 23 so far this year. "Ensuring safety is paramount in your mind. You are wearing high visibility gear, your bike is in good condition ... you are fit for the road."
The woman was wearing a helmet and had a headlight attached to her bike, but police were unclear whether she was wearing reflective gear. They expect to release her name today.
Hamilton Bicycling Network representative Bill Hope said Morrinsville Rd was a popular cycling route. He did not believe it was any more dangerous than any other in the city.
"There are a number of instances when people are in a hurry will risk a cyclist's safety in their need for speed or reducing time."
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