A heartbroken best friend swam through an acidic volcano crater to reach his colleague who was killed by a freak tsunami.

Sulphur miner, Arifin, 50, watched in horror when Andika, 61, was hit by a three-metre high wave following tremors on Mount Ijen in East Java, Indonesia, last Friday (May 30).

Andika was dragged into the abyss of 'blue fire' and his dead body surfaced the next morning.

However, brave colleague Arifin refused to wait for rescue workers to arrive with a dingy to retrieve his friend.

Arifin waved away pleas to stay on dry land and defied warnings that nobody had ever swam in the water, which volcanologists liken to ''battery acid''.

Footage shows how he stripped to his underpants and tied a rope around his waist to swim to his lifeless friend and drag the body back ashore.

Speaking after, Arifin said him and Andika had worked together for 30 years excavating sulphur.

He added: ''Andika was my best friend. We were like brothers. I could not bare the pain to see his body left in the water. I wanted him to be honoured and respected correctly. He would do this for me, too.''

Officials from the Banyuwangi SAR Independent rescue service looked on as Arifin swam through the deadly Mount Ijen crater.

They said they tried to prevent him from taking the dangerous steps but he was determined.

"I think Arifin is the first person who has dared to swim in the crater,'' one of the group told local media site Kawahijen Indonesia.

Indonesian tsunami expert Widjo Kongko said the volcano experienced tremors and the release of poisonous gas, which lead to a tsunami wave in the crater. Eyewitnesses also heard a roar before the disaster.

Widjo said: ''A tsunami may be triggered by an earthquake, landslide or volcanic activity. The phenomenon recorded in the lake within Mount Ijen’s crater is an example of a tsunami.

''Water oscillations or waves caused by tremors fall into the seiche category.''

Mount Ijen has a distinctive turquoise sulfur lake which has attracted tourists. There is also a phenomenon known as 'blue fire', which is caused by the crater’s sulfuric gas igniting as it emerges and comes into contact with the air, without producing smoke

Widjo added: "If exposed to the water in crater, the skin feels itchy. The water is similar to battery acid. This lake is definitely not recommended for swimming.'