"More than 10 people have been arrested for trying to breach the embassy," a police officer at the scene said.

A handful of protesters had gathered at the embassy, holding signs reading "The ocean is not Japan's waste bin" and "We oppose wastewater discharge."

The Yonhap News Agency said that 16 people -- all university students -- had been detained over the attempted break-in.

The students "attempted to enter the embassy office at around 1 pm (0400 GMT) while shouting slogans condemning the discharge of radioactive water," it reported.

"The police detained them on charges of trespassing and violating the Assembly and Demonstration Act."

All other protesters had been dispersed and police had restricted access to the building housing the embassy shortly after the incident, an AFP reporter saw.

Seoul has supported Tokyo's decision to release the treated wastewater from the crippled Fukushima nuclear plant, with Prime Minister Han Duck-soo saying Thursday there was "no need to be excessively concerned" about the plan.

Han also criticised what he called a "politically driven" campaign against the wastewater release, which was using "fake news" to fan fears.

There have been scattered public protests over the move, which is also staunchly opposed by the opposition Democratic Party.