A bus travelling from Bourgas to Sofia overturned at the 130km of Trakiya motorway after crashing into a traffic barrier and catching fire, Bulgarian National Television (BNT) reported on June 15 2011.

The accident occurred about 1am. Six of the 31 passengers died instantly on impact, two later in hospital in Plovdiv, and18 were seriously injured.

Twenty-two passengers were in Plovdiv`s Sveti Georgi university hospital.

The driver, a 43-year old man, had been taken into custody for 24 hours, television station bTV reported.

He said he had had no memories of the accident. His alcohol test was negative.

The crashed bus is owned by Entourtrans company and is 23 years old.

The bus had passed a routine technical check on March 8 2011, Transport Minister Ivailo Moskovski said at a briefing at the Cabinet office.

Police are investigating two possibilities; a technical problem or driver fatigue, Todor Chonov of the Plovdiv police told bTV.

During the night of June 15, in Sofia alone there were seven serious and 58 light collisions in which seven people were injured, Dnevnik daily reported.

Prime Minister Boiko Borissov has proposed June 16 as a national day of mourning, Focus news agency reported.