The Southeast Asian country has been in turmoil since a military coup that ousted Aung San Suu Kyi's civilian government, with swathes of the country engulfed in fighting.

The bombs hit a crowd queueing to drop off parcels for inmates at Insein Prison, junta authorities said in a statement, without specifying the number of explosions.

It blamed "terrorists" and said the dead included three prison staff and a 10-year-old girl.

The junta added that security forces had defused another "homemade mine" found nearby.

One witness queueing at the counter told AFP the first blast hit around 9:30 am (0300 GMT).

"Then another two went off quickly. After that we heard shooting as well," said the witness, who requested anonymity.

"I saw some people bleeding. The glass around the counter was all shattered."

According to another witness, security forces locked down the area around the sprawling, colonial-era prison after the blasts.

Pictures in local media purporting to capture the aftermath showed what appeared to be blood stains on the floor around a counter, and shattered windows behind.

There was no claim of responsibility.

A junta spokesman did not respond to a request for comment.

Inmates in Myanmar's prisons often rely on friends or family members for food and medicine supplies.

Rights groups say hundreds of political prisoners are held in Insein, including former British ambassador to Myanmar Vicky Bowman and Japanese journalist Toru Kubota.

Hearings at the special court inside the prison compound were cancelled for the day after the blasts, according to a local lawyer who did not want to give their name.

- Turmoil -

Conflict has spiralled in Myanmar since the coup.

Self-declared civilian "people's defence forces" have sprung up to fight the junta, surprising the military with their effectiveness, some analysts say.

Across the country, there are almost daily killings of low-level junta officials or anti-coup activists, with details murky and reprisals often following quickly.

While most of the violence has occurred in rural areas, Yangon has also been rocked by a spate of bombings.

In July, a bomb blast near a shopping mall in Yangon killed two people and wounded 11.

In May, a blast near a bus stop in a busy neighbourhood in the city killed one man and wounded nine people.

The junta later said the bomb had gone off accidentally and that the victim had been in contact with PDF groups it has declared "terrorists".

More than 2,300 people have been killed in the military's crackdown on dissent since the coup and over 15,000 arrested, according to a local monitoring group.

The junta blames anti-coup fighters for the deaths of almost 3,900 civilians.