"Drink in moderation and make smart decisions about how you're going to travel," senior sergeant Kelly Larsen said.
"Look after your friends as well - especially those who might have had too much to drink."
The city's cafes, restaurants and bars have been buzzing this morning with pre-races champagne breakfasts.
It will be a fine day in Christchurch today. The MetService is forecasting a high of 19C, with high cloud and a freshening north-easterly breeze.
Cup Day will include all of the usual favourite activities, outside of the actual racing, including Best Dressed Woman and Best Dressed Man competitions, and the increasingly popular body-art competition.
Gates open at 9.30am. The first race jumps at 12.05pm and the main event, the prestigious two-mile harness race New Zealand Trotting Cup is scheduled for 5.17pm.
Lazarus, with driver Mark Purdon, is the hot favourite in the $750,000 Cup.
A liquor ban is in force in the area surrounded by Lincoln Rd, Moorhouse Ave, Blenheim Rd, Matipo St and Wrights Rd.
Police say they will be stopping motorists and ensuring drivers are within the legal alcohol limits.
They have also urged racegoers to look after their belongings and minimise chances for opportunistic thieves and vandals.
"Cup and Show Week is arguably the biggest event in Canterbury's social calendar," Larsen said.
"Police want people to enjoy themselves and to remember their celebrations for the right reasons."
Meanwhile a "Drinkright Taskforce" - a team of 20 qualified duty managers from bars across Christchurch - will work with police at Cup at Riccarton on Saturday to ensure alcohol is managed responsibly, assessing patrons for intoxication and removing them as necessary.
McCall says there will be extra staff manning gates, searching vehicles and assessing patrons upon entry to the racecourse.
"The message is simple - patrons will be denied entry if they are affected by alcohol. Pre-loaders will not be tolerated," he said.
As with previous years there will be a temporary alcohol ban on the roads around the Riccarton racecourse.
BYO is no longer permitted in the members' carpark, but patrons will still be able to buy alcohol in the carpark and other licensed bar areas.
"NZ Cup Day at Riccarton is an iconic event and a wonderful celebration of racing, fashion and the best cuisine Canterbury has to offer. We want the community to be able to enjoy the day in a safe environment," said McCall.
