The rapidly expanding palm oil industry in Southeast Asia has come under attack by green groups for destroying rainforests and wildlife, as well the emission of greenhouse gases.

The blocked ships included Gran Couve, owned by the world's largest listed palm oil firm Wilmar International Ltd, which had been loading 27,000 tons of crude palm oil bound for Rotterdam, said Bustar Maitar, Greenpeace Southeast Asia, Forest Campaigner.

The other two ships blocked at the port of Dumai in Sumatra were Smooth Sea, owned by PT Musim Mas, and Victory Prima, owned by Sarana Tempa Perkasa, he said.

Greenpeace has used the tactic of seeking to block palm oil tankers previously in Indonesia, the world's biggest palm oil producer, in a bid to protest environmental concerns.

Maitar said by telephone that Greenpeace was using three rubber boats for the protest and said an activist was climbing onto the anchor of the ship Gran Couve to try and stop it departing.

Port administration officials in Dumai contacted by Reuters could not immediately confirm whether the ships were blocked.