Millions across Japan this weekend are flocking to the best spots for viewing cherry blossoms, in a tradition that last year was overshadowed by the natural disasters that struck the nation.

The national weather service announced Friday that blooming had officially started in Tokyo on March 31, using the city's central Yasukuni Shrine as a barometer -- an explosion of colours that will last only about a week.

Marking the coming of spring, the blooming of cherry trees is a beloved natural spectacle in Japan, where it sparks a nationwide string of parties and celebrations to take in the flowers' short-lived beauty.

But just weeks ahead of the annual ritual last year, a magnitude 9.0 earthquake and ensuing tsunami devastated the country's northeastern coast, leaving some 19,000 people dead and sparking a nuclear crisis.

Many cherry blossom parties were cancelled in the wake of the disaster, with one of the biggest celebrations shelved for the first time since the end of World War II.

"We weren't in the mood for partying under the flowers last year," Tokyo city official Tatsuko Suzuki told AFP at a tourism office in the traditional Asakusa district on Friday.

"Police officers from this neighbourhood were also dispatched to the disaster-hit areas, and lanterns were unlit due to the power shortage," she added, referring to red and white lanterns strung up across the nation.

Takao Yoshiya, 78, and his wife had secured a prime spot in an Asakusa park where the couple could take in a long stretch of the white and pink petals.

"We feel we can thoroughly enjoy the cherry blossoms this year, since we couldn't last year," he told AFP during a break on a flower-viewing bus tour.

"The tour takes us to eight sites in Tokyo that are famous for cherry blossoms...I can also enjoy drinking today, which I couldn't do if I had to drive."

But the full bloom had been delayed by about a week due to unusually cold March weather, while a violent storm that pounded Japan earlier this week had some wondering if the delicate buds would get blown off the trees.

"It's been so cold that we had to wait for the blooming for a long time," said 82-year-old Masako Endo, as she posed for photos with her husband and daughter.

"We were very much looking forward to this season to come."

For Kenji Niikura, a 49-year-old houseboat operator, the blooming of cherry trees, or "Sakura" in Japanese, is the most lucrative time of the year.

Cruising along Tokyo's Sumida river is one of the most popular ways to view the blooms, while enjoying a feast of sushi, tempura and lots of rice wine sake -- with a karaoke machine at the ready for red-cheeked crooners.

But this year, geopolitical tremors rather than an earthquake are affecting Niikura's business.

Western sanctions against Iran over its nuclear aspirations have helped push oil prices higher, eating away at his bottom line.

"We get about 2,000 customers a week during the hanami (viewing) season. The more frequently we operate the boats, the more fuel we use," said the seventh-generation houseboat operator.