Image copyright AP Image caption The helicopter came down on a quiet street near an apartment complex

A helicopter that had been involved in the search for missing passengers from the sunken Sewol ferry has crashed in the South Korean city of Gwangju, killing all five people on board.

The helicopter was carrying fire-fighters returning to their base when it crashed into a street near an apartment complex, Yonhap reported.

A female high school student was slightly injured by shrapnel.

Eleven people are still missing in the wake of the 16 April ferry disaster.

The fire-fighters had been involved in the search operations for the last remaining passengers since Monday, reports said.

Yonhap quoted witnesses of Thursday's accident as saying that they saw the helicopter catch fire before nose-diving into the street.

"A plume of black smoke rose with a loud bang," said an unnamed witness. "I thought it was thunder and lightning."

The cause of the accident is still unknown and officials are investigating.

Student protest

The sinking of the Sewol killed more than 300 people, most of whom were students.

The incident triggered widespread grief and anger at the government, which has promised to overhaul its bureaucracy and improve emergency response.

Image copyright Reuters Image caption Attendees of the protests in Seoul have been holding yellow umbrellas and placards

Several protests have been held in Seoul in recent days calling for an independent inquiry to be swiftly conducted.

The latest was on Wednesday when more than 30 student survivors together with their parents marched on South Korea's National Assembly in Seoul.

Their march from their high school to the building attracted hundreds of citizens who walked together with them, according to AFP news agency.

Some clutched placards with slogans such as "Truth never sinks!".

A bill that would set up an independent inquiry is currently stuck in parliament because of a split over the legal foundation.

Two separate trials, one for the ferry's captain and crew, and another for the head of the ferry operator and other company officials, began last month.