A major traffic artery through a bustling retail and restaurant strip in Sydney's inner west has been closed for more than eight hours due to an ongoing police operation.

Newtown's King Street was closed in both directions between Missenden Road and Carillon Avenue from about 11am on Monday, as police negotiated with a man on an apartment building balcony.

Police said the man does not pose a threat to the public.

The negotiations have continued throughout the day and into the evening peak, causing headaches for bus and car commuters, as well as business owners.