The sole survivor of an air crash in western Democratic Republic of Congo, in which 20 people died, remains in critical condition, reports local media.

The United Nations-funded Radio Okapi reported the woman was in intensive care in Bandundu, where the Let L-410 plane owned by Filair on Wednesday struck a building a few kilometres short of the airstrip is was attempting to land on.

The majority of those killed were Congolese.

The cause of the crash was not yet clear, although technicians at the site of the drama told Radio Okapi the flight may have run out of fuel on the hop from the capital Kinshasa.

Local authorities in Bandundu, about 200 kilometres west of Kinshasa, were still probing the accident on Thursday.

The 19-seater Let L-410 is a Czech-made twin turboprop capable of carrying up to 19 passengers and two pilots.

DR Congo's short-range air fleet consists largely of Soviet-era aircraft that are seen as being badly maintained. Air crashes are common in the sprawling Central African nation, which has poor a road network.