UPDATE 1.39pm: THE man at the centre of a siege in Brisbane has demanded a McDonald's bacon and egg McMuffin from police.

A bomb detection robot has rolled off the back of a police van at the Brisbane jetty where a man has threatened self harm, prompting officers to close down part of the city centre.

A 100-metre exclusion zone was set up around Eagle Street pier after the 54-year-old man moored his boat to the inner-city wharf and alerted police about 5am today.

Police have refused to confirm if any explosive devices have been reported onboard the yacht.

However, the man has been seen holding a jerry can and a 30cm-long bayonet.

A police officer said at the scene the man had requested a bacon and egg McMuffin.

However, the request has been made after McDonald's 10.30am breakfast cut-off time.

Police say they are trying to fulfill the request.

He also was seen playing a guitar onboard after police negotiators pulled back about 10.30am.

Police Inspector Shane Dall'Osto earlier told reporters officers hoped for a peaceful resolution.

Insp Dall'Osto refused to respond to questions about what the man's threats of self harm involved, including whether he had threatened to set alight a jerry can on board.

He said the man was alone on the boat.

Fellow yachtie and friend Mack (MACK) told reporters he was a "lovely, lovely bloke''.

"It's possibly a call for help,'' he said at the scene.

"Although he wouldn't be seeking or anticipating attention of this scale.''

The riverside walkway, Eagle Street pier, riverside ferry terminals, along with the Eagle Street city area and the Brisbane River between Holman and Thornton streets are all closed.