Heavy "automatic gunfire" rang out near the central prison in Guinea's capital early on Tuesday in Kaloum, Conakry's administrative centre, where the presidential palace is located, witnesses told AFP.

"I heard the sound of vehicles speeding by, I rushed to the window and heard automatic gunfire," said Thierno Balde, an accountant who works in the neighbourhood, confirming similar statements by other witnesses.

According to neighbours of the prison, the shooting began shortly before 9:00 am (local and GMT) and lasted just more than half an hour, with rapid gunfire ringing out.

A security detail made up of police officers and special forces blocked access to the road leading to the prison late Tuesday morning, an AFP journalist saw.

An armoured vehicle belonging to the special forces was also visible in front of the jail.

Abdouramane Doukoure, a retired civil servant, said he was heading past the prison in a car when he "heard the gunshots. Since there was a traffic jam, we all rushed in different directions to escape."

Another resident whose home is next to the prison reported hearing gunfire inside the facility, but "as we speak, things have calmed down".

But "we don't know for how long", the resident added.