(MANILA) - Toxic pesticides inside the hull of a sunken Philippine passenger ferry could start leaking any time, European Union experts warned Friday.

Their findings showed "no observable oil sheen or environmental pollution" so far but they warned this could soon change.

Releasing the findings, the undersecretary for Philippine maritime affairs Maria Elena Bautista said "there is really no assurance that the packaging will hold after more than a month."

The Princess of the Stars sank during a typhoon on June 21 off the central island of Sibuyan with over 800 aboard.

As divers began retrieving bodies from the vessel it was revealed it was also carrying a cargo of the deadly pesticide Endosulfan, threatening the rich fishing waters around the island.

The government also found the ship was carrying smaller amounts of other deadly pesticides.

Of the passengers and crew, just 57 people survived the tragedy and hundreds of bodies remain trapped inside the ferry.

Government agencies will continue to do tests off the waters around the shipwreck and the currents passing through the area to make sure the waters are still safe.

As a precautionary measure, a five-kilometre (3.1-mile) zone has been set up around the shipwreck where boats and fishing are not allowed, officials added.

EU salvage expert Rune Stefan Berglind warned that the government must have contingency plans in place in case the ship starts to break up or if another typhoon hits the area.

He said that the government's handling of the situation was "well done so far," but stressed that a masterplan must be ready to remove the toxins from the water.

The UN and EU are willing to dispatch more experts to the country to help in addressing the problem if needed, officials said.

Bautista said the owner of the sunken ferry, Sulpicio Lines, had selected a foreign company to salvage the ship and the removal of the chemicals will start on August 4 and last for about 30 days.

She criticised Sulpicio Lines for not doing enough to salvage the ferry and minimise the damage.

"They can do more," she said but declined to elaborate.

The sinking of the ferry has become one of the country's worst maritime disasters and is just the latest in a string of sea tragedies involving Sulpicio Lines vessels.

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