(Reuters) - Calgary, the largest city in Canada's primary oil-producing province of Alberta, has declared a state of local emergency due to ongoing repairs on the city's main water pipeline which ruptured last week, the mayor announced on Saturday.

Residents face a critical water shortage and urgently need to reduce their water usage, Calgary Mayor Jyoti Gondek said.

Water restrictions in Calgary could remain in place for a month or longer, after an internal analysis of the ruptured water pipeline identified five additional "hot spots" at risk of failure, Gondek said.

"This is not a decision that was made lightly, but as we shared yesterday at 5 p.m., the investigation of the broken feeder main pipe revealed that there are five more areas that need repairs," Gondek said.

"We are going to need to reduce water use and I rely on you so that we can get through this," she said.

The rupture last week in the city's main water feeder, which carries water supplies to 1.2 million people, flooded streets, playing fields, and a section of the TransCanada highway, the country's main east-west route, which remains closed.

Downtown Calgary is home to the vast majority of Canada's oil and gas companies.

Outdoor watering is banned and residents have been asked to delay using dishwashers and washing machines and limit shower times.

The 11-kilometre pipeline, known as a feeder main, was installed in 1975 and is one of the most important and largest water supply arteries in Calgary.

The Calgary Emergency Management Agency's chief Susan Henry said that the repair process will be complex.

"We are working as hard as we can to bring that timeline down," she said.

The announcement comes less than three weeks before the start of Calgary's annual Stampede event, a 10-day celebration of rodeo and western cowboy culture that brings hundreds of thousands of visitors to the city.

(Reporting by Wa Lone; Editing by Chizu Nomiyama)

By Wa Lone