Burma's President Thein Sein has declared a state of emergency and imposed martial law in a region near the Chinese border after more than 70 people were killed in fighting between the Burmese army and a rebel group.

The conflict is a setback for Burma's semi-civilian government, which took power in 2011 after 49 years of military rule and is seeking to end hostilities with the many groups that have taken up arms since independence in 1948.

The clashes in the Kokang region of Shan State in Burma's northeast have alarmed China, which has called for a ceasefire.

China fears a repeat of events in 2009, when tens of thousands of civilians crossed the border to escape fighting.

Burma's president declared martial law for three months in a televised announcement, the first time military rule has been invoked under Myanmar's 2008 constitution.