Excessive land reclamation from the sea poses a growing threat to oceanic ecology and aggravates coastal pollution, a top administrator has warned.

Sun Zhihui, head of the State Oceanic Administration (SOA), said strict laws to protect arable land have prompted local authorities to resort to sea reclamation to meet growing land demand.

"China is experiencing a new wave of land reclamation in its coastal regions," he told China Daily.

Reclaimed land accounts for 3 to 4 percent of the mainland's total new construction area annually. In coastal provinces and municipalities, the figure is 13 to 15 percent.

From 2002 to 2009, 74,100 hectares of land was reclaimed from sea, mainly for construction of industries, tourism and ports, according to the SOA.

Projects on reclaimed land are much cheaper than on land. Generally, the cost per square meter for sea reclamation ranges from 220 yuan ($32) to 520 yuan, while building on land costs thousands of yuan because of expenditures on relocation.

The State Council has so far approved seven coastal economic zones in Liaoning, Hebei, Tianjin, Jiangsu, Fujian, Guangdong and Guangxi and two are being planned in Shandong and Zhejiang, Sun said.

Sun, however, warned that land reclamation may go out of control due to the absence of a national macro-control scheme.

"Overdevelopment of coastal zones can bring adverse effects such as environment degradation and seafood pollution," Sun said.

As a majority of heavily-polluting chemical, energy and transportation industries are in coastal areas, a variety of pollutants like heavy metals and organic toxins are discharged into the sea with wastewater.

According to an inspection last year, about 74 percent of 457 discharge outlets released excessive pollutants, with 14 million tons of heavy metals discharged into the ocean, a year-on-year increase of 16 percent, official figures showed.