DALIAN - Authorities in northeast China said that the dike breached by powerful waves earlier Monday has been temporarily blocked after workers dumped trucks of rocks and concrete to repair the breach.

The breach has sparked fears of a toxic spill from a petrochemical plant located behind the dike.

Twenty-meter-high waves, spawned by tropical storm Muifa off the coast of north Liaoning province, broke a dike in the Jinshan Industrial Zone in the city of Dalian Monday morning, threatening to hit the Fujia chemical plant just 50 meters behind the dike, said a spokesman with the emergency response headquarters.

As of 3 pm the two breaches, which measured at least 20 to 30 meters long each, have been temporarily blocked, but workers still fear that the strong waves might wash away the loosely piled rocks and breach the dike again, said the spokesman.

Trucks are still dumping rocks and concrete to make the newly repaired parts solid, he said.

Authorities have not specified which chemicals may be a risk of leaking from the plant. The Fujia chemical plant is a producer of paraxylene, a petrochemical used to create raw materials for the production of polyester film and fabrics. The chemical is carcinogenic.

Residents in nearby areas are being evacuated.

The plant is transporting the toxic chemicals out of the tanks near the dike, said the spokesman.

Tropical storm Muifa, previously a typhoon, is expected to make a landing near the border of the Democratic People's Republic of Korea (DPRK) and Liaoning on Monday afternoon, according to local weather forecasts.

More than 490,000 people have been evacuated in Liaoning Province and the eastern province of Shandong as of Monday afternoon, as Muifa continues to move along the country's eastern coast.