Japanese tour agencies are bracing for an influx of millions of tourists at parks nationwide during the annual cherry blossom season as enthusiasm around the flower-viewing festival has doubled on social media since last year.

In 2015, a record 19.73 million overseas tourists visited cherry blossom hotspots in at least 18 park-hosting cities throughout Japan.

This year Osaka-based tour agency Freeport Inc., which offers tours to the historic Osaka Park Castle, says it is already 80 percent booked through to mid-April, the Yomiuru Shimbun reports.

The surge comes at a time when social media buzz on Chinese micro-blogging site Weibo has doubled since last year, with nearly 19,000 posts about the event in February alone.

The centuries-old festival, known locally as hanami, is celebrated with picnics and outdoor parties beneath the blooming sakura, or cherry, trees to recognize "the fragility and transience of life".

"The sakura flowers reach almost divine beauty for only a dozen days a year, before they wither," writes Kyoto-based tour operator Japan Experience on their website.

This year the flowers are expected to bloom Tuesday in eight southern cities - including Tokyo, Nagoya, Kumamoto and Fukuoka - before moving northwards to prefectures home to cities including Sapporo and Yoshino, according to the Japan Meteorological Agency.

"We have high hopes for this year's hanami sales offensive," said a park official from Ueno Park in Tokyo, adding that the park last year received 2.34 million visitors and in 2016 has planned additional events including allowing visitors to practice throwing ninja stars, or shuriken, a flat-bladed weapon popularized overseas through comics. EFE