At least four more officials of the sunken South Ferry passenger ferry Sewol have been arrested on charges of overloading the ship with cargo. Retrieval operations, meantime, continued even as divers rallied on despite the death of a civilian colleague.

On Tuesday, South Korean officials formally identified cargo overloading as the most probable cause for the ferry disaster that claimed 267 lives.

"We are still calculating exactly how many tons of cargo the ship was carrying, but based on what we have found out so far, it's clear that it was carrying more than allowed," the Globe and Mail quoted Yang Joong-jin, a senior prosecutor involved in the investigation.

Initial investigation showed the Sewol suddenly listed on April 16 and then began sinking when it made a sharp turn while it battled a strong current. Later inquiry found the ship added cabins in the upper deck so that it could increase passenger capacity to 921 from 804. This made the ship's top too heavy thus impairing its ability to right itself after tilting.

It was also learned the Sewol carried far too many vehicles, shipping containers and other cargo on board. These were poorly tied down so that when the tilting happened, the ship failed to recover its balance.

Read: South Korea Ferry Disaster: Video Footage Showing Final Moments of Students Onboard Released (PHOTOS/VIDEOS)

The four officials arrested included a 62-year-old executive of Chonghaejin Marine Co., operator of the 6,825-tonne Sewol.

A day before Sewol embarked from Incheon, its officials reported to the shipping association that it has 657 tonnes of cargo and 150 vehicles. The Globe and Mail reported that after the accident, Chonghaejin revised the data to 124 cars and 56 trucks and 1,157 tonnes of cargo.

Meantime, divers continued their retrieval operations for the still missing 35 others despite the death of a civilian colleague on Tuesday.

Lee Kwang-wook, a 53-year-old civilian diver from Undine Marine Industries, fell unconscious at 6:05 am shortly after plunging into the waters which was around 25 metres deep.

The veteran diver was immediately rushed to a nearby hospital where he was pronounced dead. Mr Lee is the first diver fatality killed during the search and retrieval operations of the Sewol ferry disaster. The cause of his death is currently under investigation.

South Korean Prime Minister Chung Hong-won immediately ordered a thorough check on the health of divers participating in the search and retrieval operations.

A boy ties a yellow ribbon dedicated to missing and dead passengers of the sunken passenger ship Sewol on a pillar at Yellow Ribbons Garden set up at Seoul City Hall Plaza May 5, 2014. A culture of cosy personal ties that can blur the lines between busin
A boy ties a yellow ribbon dedicated to missing and dead passengers of the sunken passenger ship Sewol on a pillar at Yellow Ribbon's Garden set up at Seoul City Hall Plaza May 5, 2014. A culture of cosy personal ties that can blur the lines between businesses and those regulating them, of profit over safety, and soft courts is in focus as South Korea demands answers over the sinking of a ferry with the loss of more than 300 lives, mainly high school students. REUTERS/Jung Hwe-sung/News1 REUTERS/Jung Hwe-sung/News1
People and family members of missing passengers onboard the sunken passenger ferry Sewol release paper lanterns in memory of the missing and dead passengers, at a port where family members of missing passengers are gathered in Jindo May 6, 2014, on the oc
People and family members of missing passengers onboard the sunken passenger ferry Sewol release paper lanterns in memory of the missing and dead passengers, at a port where family members of missing passengers are gathered in Jindo May 6, 2014, on the occasion of Buddha's birthday. The Sewol ferry sank on a routine trip south from the port of Incheon to the traditional holiday island of Jeju on April 16. More than 300 people, most of them students and teachers on a field trip from the Danwon High School on the outskirts of Seoul, have died or are missing and presumed dead. REUTERS/Yonhap REUTERS/Yonhap
Buddhist monks, believers and family members of the missing passengers onboard sunken passenger ferry Sewol march during a service in memory of the missing and dead passengers at a port in Jindo May 6, 2014, on the occasion of Buddhas birthday. REUTERSY
Buddhist monks, believers and family members of the missing passengers onboard sunken passenger ferry Sewol march during a service in memory of the missing and dead passengers at a port in Jindo May 6, 2014, on the occasion of Buddha's birthday. REUTERS/Yoo Seung-kwan/News1 REUTERS/Yoo Seung-kwan/News1
A hyperbaric chamber is seen at a port at a port where family members of missing passengers of the sunken passenger ship Sewol are gathered in Jindo May 6, 2014. A civilian diver taking part in the search for those missing from a recently sunken ferry die
A hyperbaric chamber is seen at a port at a port where family members of missing passengers of the sunken passenger ship Sewol are gathered in Jindo May 6, 2014. A civilian diver taking part in the search for those missing from a recently sunken ferry died Tuesday after falling unconscious during a mission, officials said. REUTERS/Yoo Seung-kwan/News1 REUTERS/Yoo Seung-kwan/News1
A boy sits next to a board with messages written for victims of sunken passenger ship Sewol, outside the official memorial altar in Ansan May 2, 2014. A culture of cosy personal ties that can blur the lines between businesses and those regulating them, of
A boy sits next to a board with messages written for victims of sunken passenger ship Sewol, outside the official memorial altar in Ansan May 2, 2014. A culture of cosy personal ties that can blur the lines between businesses and those regulating them, of profit over safety, and soft courts is in focus as South Korea demands answers over the sinking of the ferry with the loss of more than 300 lives, mainly high school students. REUTERS/Kim Hong-Ji REUTERS/Kim Hong-Ji
South Korea