The oil spill around a sunken Iranian tanker in the East China Sea has tripled in size in recent days, China's State Oceanic Administration said Monday.

Three slicks with a total surface area of 332 square kilometers (128 square miles) have been observed, compared to 101 square kilometers last Wednesday.

That means the oil slick is now about the size of Malta.

The tanker Sanchi was carrying 111,000 tons of condensate when it collided with a Hong Kong-registered grain freighter on January 6. After burning for days it sank on January 14.

All 32 sailors on board perished.

Read more: Sunken oil tanker: How to protect the high seas environment

Condensate does not form a traditional oil slick, but can be highly toxic to marine life.

When at the surface it can burn off or evaporate in the air.

However, some scientists have warned that the condensate will remain invisibly toxic underneath the water.

The extent of the environmental damage depends on how much of the condensate burned off or evaporated at the surface before the ship sank, as well as how much is leaking underneath the water.

It was the largest condensate spill on record.

cw/rt (AFP, AP, dpa)