SEOUL (AFP) - Bad weather and high tides have again delayed the resumption of operations to raise South Korea's sunken Sewol ferry, the Maritime Ministry said on Monday (June 27).

After already being pushed back once due to bad weather, the salvage operation had been scheduled to resume on Tuesday but has now been put off for another two weeks.

"The operations for raising the bow and installing lifting beams have been inevitably delayed to July 11 due to bad weather, including high tide and winds," the ministry said in a statement. "Because the lifting of the bow section is a very challenging operation... it can only be conducted when the tide is below 1m."

The vessel was carrying 476 people when it went down off the southwestern island of Jindo in April 2014, leaving 304 people dead - mostly school children - in one of the country's worst maritime disasters.

The tide is forecast to be around 2m to 4m in the next few days, according to the ministry.

It is thought that nine bodies still unaccounted for may still be trapped inside the sunken ship, and raising the ferry intact was a key demand of the victims' families.

The 6,825-tonne ferry lies more than 40m below the surface and the process of actually lifting it off the seabed began earlier this month - only to be suspended a day later due to adverse weather conditions.

The salvage effort is expected to cost around US$72 million and is being led by a Chinese consortium.

The initial schedule envisaged bringing the ferry to the surface by late July, but the ministry later revised its likely timeline to August - depending on conditions during the July monsoon season.

Investigations into the Sewol disaster concluded it was largely a man-made tragedy - the cumulative result of an illegal redesign, an overloaded cargo bay, inexperienced crew and a questionable relationship between the ship operators and state regulators.

Captain Lee Jun Seok was sentenced to life in prison for "murder through wilful negligence" and sentences ranging from two to 12 years were handed down to 14 other crew members.