Japan's brewers, fierce rivals as they fight for share of the country's stagnant beer market, are reportedly set to join forces in a campaign to boost sales.

The country's top five brewers - Kirin Brewery Co., Asahi Breweries, Sapporo Breweries, Suntory and Orion Breweries - have formulated plans to create an annual special week of beer.

According to local news agency Kyodo News, a week in late May will be dubbed "Beer-den Week" when there will be a series of promotional activities.

"The Golden Week holidays that everyone knows in Japan are in early May. Now we want to propose that late May is Beer-den Week, a season to enjoy beer by feeling the coming of early summer," the report quoted Sapporo president Masaru Fukunaga as saying.

To promote the week, the brewers said will organise a four-day event at Tokyo's Roppongi Hills from 24 May, the report added.

Last year, Asahi managed to hold on to the top spot in the Japanese beer market despite fierce competition from Kirin.

Asahi leads the Japanese beer market in terms of shipments, selling 187.4m cases last year. Kirin saw sales rise for a second successive year in 2006, reaching 187.1m cases, a climb of 4.8%.