Greenpeace activists Wednesday protested plans by Indonesia to build Southeast Asia's biggest coal power plant, saying it would sully coastal waters and strip the livelihoods of fishermen and farmers.

Masked activists from the environmental group, dressed in black, marched alongside a replica of a sinking ship through the capital Jakarta to the Maritime and Fisheries Ministry, calling for the project to be scrapped.

Greenpeace said the planned coal plant in central Java's Batang district would pollute coastal waters and threaten the livelihoods of more than 10,000 fishermen as well as farmers on nearby lands.

Greenpeace campaigner Arif Fiyanto noted that Indonesia had committed to reducing its greenhouse gas emissions by 26 percent from 2009 levels by 2020.

"But coal contributes 60 percent of global emissions," he said. "If Indonesia were serious about its commitment, it would try to reduce the country's dependence on fossil fuels."

The Indonesian government says the planned coal plant would be the biggest in the region, and with a capacity of 2,000 megawatts (MW) would boost the country's bid to add 20,000 MW to its grid from 2005 levels by 2016.

The plant is set to be built in a public-private partnership between Indonesian coal miner Adaro Energy and Japan's Electric Power Development (J-Power) and Itochu Corp., after the consortium won a $3.2 billion tender last year for the project.

Greenpeace activists called the project "illegal", arguing that the coastal area of Ujungnegoro-Roban to be developed was actually protected territory under a central government regulation from 2008.

But Batang's district government issued a new regulation in 2011 stating the area was no longer protected -- and a maritime ministry official said Jakarta had no authority to overrule the decision.

"Indonesia is a democracy, and our country decided to give more power to local governments to make these decisions," Sudirman Saad, the ministry's head of marine, coastal and small island affairs, told Greenpeace and reporters.

"This isn't our responsibility. If you want to ask why this project was approved, you have to ask the Batang government," he said.

Indonesian delegates at the Rio+20 environmental summit in Brazil last month stressed the importance of a "blue economy" to help tackle climate change and conserve marine resources in the world's biggest archipelagic nation.