South Korean dive teams struggled today to gain access to blocked cabins of a submerged ferry that sank nearly three weeks ago.

The confirmed death toll from the disaster rose to 242 as six more bodies were recovered early today.

It was 18 days ago when the 6,825-tonne Sewol vessel capsized and sank with 476 people on board. Sixty people are still unaccounted for.

"Rescuers using some equipment are trying to open blocked cabins," spokesman Ko Myeong-Suk told a morning briefing.

The search has been hampered by fast currents and high waves, while dive teams have been working in challenging and sometimes hazardous conditions.

They have to grope their way down guiding ropes to the sunken ship, struggling through narrow passageways and rooms littered with floating debris in water.

As days go by, personal belongings and other items from the ship have been spotted further and further away, fuelling concerns that some victims of the ferry disaster may never be found.

One body was retrieved Friday by a fishing vessel two miles away from the recovery site, and another was found a mile away on Wednesday.

As a precaution, recovery workers have put rings of netting around the site.

Bedding materials from the ship were found as far as 30km from the disaster site on Friday.

It is one of South Korea's worst peacetime disasters, made all the more shocking by the loss of so many young lives.

Of those on board, 325 were students from the same high school in Ansan city, just south of Seoul.

Public anger has focused on the captain and crew members who abandoned the ship while hundreds were trapped inside.

Authorities have also been criticised as more evidence emerges of lax safety standards and possible corruption among state regulators.

The captain and 14 of his crew have been arrested.

The Sewol's regular captain, who was off duty on the day of the accident, has said the Chonghaejin Marine Co ferry operator "brushed aside" repeated warnings that the 20-year-old ship had stability issues following a renovation in 2012.

Two Chonghaejin officials were arrested on Friday on charges of having the ferry overloaded well beyond its legal limit.