The St. Petersburg to Tallinn Ecolines bus left the road around 30 kilometers from Tallinn, and rolled on to its side, at 4.45 a.m. Sunday morning, ERR's online news in Estonian reports.

Nine people were taken to hospital, none with life-threatening injuries. Four of the injured were Latvian citizens, it is reported.

The remaining passengers were taken onward to Tallinn on a replacement bus. The crashed bus was later towed away (see gallery).

Ivo Utsar of the Police and Border Guard Board's (PPA) northern prefecture said that the driver was found to have no traces of alcohol in his system, and had been wearing a seatbelt at the time of the accident. How many passengers were also wearing seatbelts is not yet known.

Early indications suggest technical failure of the bus causing the driver to lose control, though an investigation is underway.

However, Ecolines spokesperson Elis Kovaljov told news portal Delfi that a collision with either an obstacle or a wild animal on the road was behind the accident.

"Because it was dark and the weather was so bad, the bus driver couldn't spot [the obstacle] quickly ... hence why the bus slipped off the road and, due to slippery conditions, the bus rolled over," Kovaljov said.

Road maintenance company Üle OÜ says however that the road had been salted, and was wet, rather than slippery, a line backed up by the Road Administration (Maanteeamet).

"Despite the fact that today's accident could have been caused by various factors, passengers can always do a lot to maximise their safety Right from sitting down at the start of a journey, you should fasten your seat belt," said Ivo Utsar.

The PPA asks any witnesses to call 112; passenger luggage left behind at the scene can be reclaimed by contacting the Ida-Harju PPA station at P. Pinna 4 in Tallinn.

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