An oil slick from a stricken cargo ship off Taiwan's north coast could cause "massive" devastation to the area's sea life, environmentalists said Friday, as clean-up workers scrambled to contain the leak.

Bad weather is hampering more than 100 workers who are trying to contain the slick after the Taiwanese ship "T.S. Taipei" became stranded on a reef earlier this month off the shore of Shihmen in New Taipei City.

"Even if the oil stains can be removed swiftly, massive deaths of fish and other marine animals in the area are expected due to lack of oxygen in the water," said Michael Lee, secretary-general of the non-profit Society of Wilderness (SOW).

"It could take at least three years for the local ecological system to recover to some extent," he added.

Around 1.9 kilometres (1.18 miles) of coastline has already been polluted since the ship ran aground on March 10 and workers in protective gear were using buckets and solvents Friday to remove oil from the shore.

A salvage operation has been trying to drain the ship's oil tank, but has been hampered by bad weather.

There are still over 200 tonnes of fuel and 614 cargo containers with machinery, furniture, textiles and other items on board, as well as nine containers containing lubricant and toxic chemicals, said the Environmental Protection Administration (EPA).

"The ship has fractured down the middle and could capsize anytime... if it capsizes, the remaining fuel could leak out and the cargo containers will fall into the sea, affecting the local coastline and ocean habitat," it said in a statement.

The worst oil spill in Taiwan in recent years was when Greek-registered Amorgos, carrying 60,000 tonnes of iron ore, ran aground off the southern coast in 2001.

Nearly 1,000 tonnes of oil gushed out of the vessel, contaminating a coastal reserve and seriously damaging the area's ecosystem.