A plane has crashed in the north of South Sudan killing at least 20 people, Unity state minister for information said on Wednesday.

The aircraft came down near the oil fields in Unity State at around 10:30 am local time (0830 GMT) shortly after taking off for the capital Juba. 

"The plane crashed 500 metres away from the airport. 21 people were on board. As for now, there's only one survivor," Gatwech Bipal Both told AFP by phone.

He said the aircraft, chartered by the Greater Pioneer Operating Company (GPOC) and operated by Light Air Services Aviation Company, was on a routine mission to the area. 

"The state government is in a deep sorrow by this accident", he said, saying there would be an investigation.

"Although most people predicted that this might be a mechanical collision."

South Sudan, a young nation that achieved independence in 2011 and has been in the throes of a chronic economic and political crisis, lacks reliable transport infrastructure, with plane crashes often blamed on overloading and poor weather.