Police have "serious concerns" about a radio station's promotion of a day devoted to drinking up to 9 litres of beer.

Crate Day is a "tradition" where people drink a "swappa crate" – 12 large (745-millilitre) bottles of beer – to celebrate the beginning of summer.

Although the crates are marketed to be shared, many participants see it as a challenge to drink 9 litres on their own.

Assuming the beer is 4 per cent alcohol by volume, that's close to 30 standard drinks.

READ MORE:

* Police slam Crate Day participants

* Man wakes from coma after Crate Day fall

* Mediaworks warns NZBlokes over copyright of beer event

Police say they have "serious concerns" about the event.

VIRGINIA WOOLF Police conduct a scene examination at an incident in which a 20-year-old man suffered serious head injuries on Saturday night in Headingly Lane, Richmond.

"We have serious concerns about any event like this which encourages binge drinking and could put participants and other members of the public at risk," a police spokesperson said.

Police were unable to say how many callouts or drink-driving incidents during the day involved Crate Day participants, however anecdotal reports from police districts suggested there were "some incidents".

Timaru's Sergeant Greg Sutherland said police on Saturday responded to three callouts where people were driving drunk and erratically. All of the drivers were participants of National Crate Day.

A Nelson man was on life support with a brain bleed after falling from the back of a ute and hitting his head on the road. The 20-year-old had been partying with friends who were taking part in National Crate Day.

Mediaworks radio station The Rock FM has organised the event since 2010. The branding strategy involved in-store deals at Super Liquor.

On its website, The Rock FM said the event was created by host Duncan Heyde.

Mediaworks has taken ownership of the day, even defending the term "NZ Crate Day" when a men's lifestyle website created a Facebook event under that name.

Mediaworks said the meet-up sounded too similar to The Rock FM's National Crate Day.

In a letter, the company said the term was "clearly associated with New Zealand" and "enjoys significant goodwill and reputation in both the National Crate Day concept and associated intellectual property".

Mediaworks did not respond to a request for comment on Monday.