Russian investigators say a bus with construction workers has driven off a pier in southern Russia, killing 14 and leaving three others missing.

The Investigative Committee says the bus had been carrying workers who were building a pier for an oil company on the Black Sea coast not far from Crimea. The Emergency Situations Ministry said 20 people have been rescued, and scuba divers are searching the waters for three missing men.

Investigators didn't immediately give a cause for why the bus drove off the pier Friday morning.

"The bus was carrying 35 people... 12 of them died. Twenty were rescued. Three people are missing, the search for them is ongoing," it said, quoting a representative of the Krasnodar region emergency ministry.

Divers are working at the scene of the accident, where the bus plunged four metres before hitting the water, a source told RIA-Novosti news agency, saying it was likely caused by a traffic violation.

The accident occurred on the Taman peninsula on the Black Sea near the Strait of Kerch that flows between Russia and the Crimean peninsula.