Brazilian authorities are scrambling to avert an environmental disaster after an oil tanker sank to the bottom of a river in the Amazon jungle.

The 70m (230 foot) barge, operating under contract for Texaco, sank last Friday while its crew were loading 14,000 barrels of heavy fuel oil.

The submerged barge was sitting upright 10m (30 feet) below the surface of the Rio Para near Belem, 2,350km (1,460 miles) north of Sao Paulo.

Although the barge sank with 1.8m litres (470,000 gallons) of oil aboard, port authorities said there were no signs of leaks.

Diving teams have removed the vessel's tanks, while Texaco and state environmental officials launched floating walls to prevent any potential spill from spreading upriver.

"Environmental advisers are working alongside the diving teams to prevent ecological damage," said Mauricio Andres Ribeiro, of Brazil's environment ministry.

Texaco spokesman Harry Rich said salvage teams may either refloat the barge or pump out the oil and transfer it to another vessel.

Another company official said there was little risk of a leak, as the cooler temperatures at the bottom of the river had thickened the oil.

Major spill

The accident came just two weeks after a major oil spill in Rio de Janeiro, when a burst pipeline at state oil giant Petrobras' flagship refinery spewed 1.3m litres (345,000 gallons) of fuel into the picturesque Guanabara Bay.

The leak destroyed local fishing industry, contaminated biological reserves and killed wildlife in the area's worst ecological disaster in 25 years.

Petrobras was fined $28m for the accident, and officials said they have not ruled out similar sanctions in the case of the Amazon wreck.

"There will be a study on the accident's causes and damage, and if damages to the ecosystems in the area are determined, there will be a fine," Mr Ribeiro said.

Texaco has contracted Smith American Inc and Oil Spill Response Ltd to co-ordinate the clean-up operation