(Adds details from Cuba, Cayman Islands and Jamaica)

Jan 28 (Reuters) - A powerful magnitude 7.7 earthquake struck in the sea south of Cuba on Tuesday, triggering a tsunami warning for Cuba, Jamaica and the Cayman Islands, the U.S. Geological Survey (USGS) and the International Tsunami Information Center said.

The epicenter of the quake, initially reported as magnitude 7.3 before being upgraded, was between Jamaica, the Cayman Islands and Cuba, at a shallow depth of 6.2 miles (10 km).

The quake was not strongly felt in the Cuban capital of Havana or in Kingston, Jamaica, according to Reuters witnesses.

Meanwhile, Mikhail Campbell, a police media relations officer in the Cayman Islands, said he was not immediately aware of any reports of serious damage.

Tsunami warnings were quickly issued.

"Hazardous tsunami waves from this earthquake are possible within 300 km (186 miles) of the epicenter along the coasts of Jamaica... Cayman Islands and Cuba," the International Tsunami Information Center said.

The disaster management agency for the Cayman Islands government on Twitter urged people to move away from coastal areas and said that those in low-lying areas should "evacuate vertically" in strong multi-story buildings. (Reporting by Mekhla Raina in Bengaluru and Dave Graham in Mexico City; Editing by Bernadette Baum, Sandra Maler and Nick Zieminski)

Our Standards: The Thomson Reuters Trust Principles.