SINGAPORE, April 13 (Xinhua) -- Singapore's Asia Pacific Resources International Group (APRIL) signed an agreement on Wednesday to boost its investment in a pulp and paperboard mill in China's eastern province of Shandong by 30 billion yuan (4.6 billion U.S. dollars).

The phase three investment by the subsidiary of Royal Golden Eagle Group (RGE Group) in the mill in the city of Rizhao is also the largest investment by a foreign firm in Shandong, one of the coastal provinces that has been leading the economic growth of the country over the past decades.

Huang Jinping, co-president of RGE Management China, said the phase three investment, subject to approval by authorities, mainly includes a second production line for high quality paper board and additional high quality paper production capacity.

It will increase the annual pulp production capacity of its Rizhao plant by about 1 million tons and its production of paper and paperboard by about 2.4 million tons, he said, adding that the first two phases of the mill is now running in close to full capacity.

When the phase three development is completed, the Rizhao mill will have an annual capacity of 3 million tons of pulp and 3 million tons of paper and paperboard.

RGE Group had previously invested a total of 15 billion yuan (2. 3 billion U.S. dollars) to upgrade and expand the pulp mill it acquired in Rizhao, Shandong, in 2005.

The mill is "one of the largest and most technologically advanced operations of its kind in the world. Our operations in China include significant investment in environmental technology to ensure that we are energy efficient and environmentally responsible," Huang said upon signing the agreement in Singapore.

RGE Group, a resources conglomerate, has been making many investments across China. Huang said the mainland market is now one of the most important drivers of growth for the group.