District road policing manager Inspector Leo Tooman said police were investigating claims the Honda and Subaru were racing and the drivers of both cars were being interviewed.
The innocent driver of the third vehicle would also be interviewed, Mr Tooman said.
Less than an hour earlier, a 42-year-old man died after his silver Porsche Boxster convertible crashed on Waring Rd at Taupiri.
Mr Tooman said the car was "travelling at speed when it has left the road, gone down a bank and crashed through a number of trees before coming to a rest in a paddock".
The man died at the scene.
Mr Tooman said the deaths left "chilling warnings" on the eve of the long weekend.
"Both crashes are being investigated by the Waikato Serious Crash Unit and initial indications point to speed being contributing factors in both," Mr Tooman said.
"The official holiday period begins at 4pm today and we can expect a combination of higher than usual traffic flows at the same time as varied weather conditions.
"We want people out on Waikato roads to drive to survive and avoiding excessive speed will play a major part in this."
The deaths give Waikato the unenviable record of having the country's highest road toll.
So far this year 34 people have died in 31 crashes on the region's roads, two more than the Central District.
"Of those crashes, a number involved alcohol as a contributing factor including a triple fatality in June," Mr Tooman said.
"With this holiday weekend being the first in four months, we're asking drivers to reduce the risks on the road by avoiding alcohol.
"It's definitely a case of throttle or bottle, not both - the two don't mix."
Police will have a large presence on Waikato roads this weekend, he said.
Last year 22 people died in 18 crashes in Waikato where alcohol, drugs or both were contributing factors.
During the Labour Day long weekend last year, the Waikato district recorded one fatality.
