Three Thai men died after being overcome by powerful fumes from rotting fish in a boat they were unloading in Perak, reports said today.

Another Thai crewman who tried to pull them to safety narrowly escaped death himself but was able to crawl out of the hold in time, Perak police official Zainuddin Yaakob told the Bernama state news agency.

Zainuddin said the four men were unloading the boat at a jetty when one of them was instructed to go into the hold which also contained rotting fish that had spoiled after the cooling system failed.

"Upon entering the hold, he must have breathed the fumes emitted by the rotting fish," he said.

When the three others realised their friend had collapsed, they rushed down to help but were themselves overcome by the stench.

The survivor, 31-year-old Yong Chai, told reporters that the tragedy happened extremely quickly.

"When the three of us entered the boat's hold, I saw my friend lying on the floor and frothing at the mouth. Then my other friends started collapsing one after another, and lost consciousness," he said.

"When I realised I had difficulty breathing, I quickly crawled out of the hold and sought assistance from other workers."

Zainuddin said all the Thais had valid work permits and travel documents, and police did not suspect foul play.