An algae bloom, or "green tide," has quickly expanded across 35,000 square km of waters off China's eastern coast, the country's maritime authorities said Wednesday.

The North China Sea Marine Forecasting Center of State Oceanic Administration reports the algae bloom grew from 1,500 square km on May 22 to 35,000 square km on June 4.

The algae cluster is moving northeast, posing threats to coastal areas of east China's Shandong Province, where the local economy depends heavily on aquaculture and tourism.

Though the green algae is not poisonous, it can block sunshine and consume large amounts of oxygen, suffocating marine life. The algae bloom can also choke shipping channels and create a bad odor if washed ashore.

The green tide first emerged in the Yellow Sea in 2007, baffling local residents. Since then, it has occurred nearly every summer.

The algae develops by absorbing nitrogen and phosphorus pollutants in sea water. Its bloom is also be driven by temperature changes. The algae bloom this year may be more serious than before, according to the monitoring center.

Authorities in Qingdao, a coastal city in Shandong, have mobilized locals with sea vessels to help remove the algae

Through the years, locals have developed ways to recycle the collected algae into fertilizer, animal feed and food additives.