Explosions killed at least five people and injured 50 in Burundi's largest city Bujumbura on Monday night, a health worker told Reuters after the latest in a string of attacks in the east African country.

The Interior Ministry put the death toll at two and said on Twitter that "unidentified terrorists" were responsible.

Two grenade explosions hit a bus parking lot in the city centre, according to seven eyewitnesses, while a third blast hit Jabe market in the Bwiza neighbourhood, according to another witness.

Five people were killed and about 50 injured, a health worker helping to care for the injured told Reuters on Tuesday. Like the witnesses, the health worker asked for anonymity for fear of reprisals for talking to media.

A man in a bus hit by a grenade explosion said it killed at least three people including a woman. The blast injured his leg, he told Reuters while awaiting treatment.

Prime Minister Alain-Guillaume Bunyoni's office said on Twitter he had visited the wounded in hospital and promised them government help.

(With input from agencies)