Dear city, sorry we made you grind to halt at rush-hour. Yours truly, trams chief

Buses were delayed by about an hour by the complete closure of the main junction at The Mound.

Transport chiefs admitted defeat by mid-afternoon and crisis talks led to the westbound route being reopened to buses in time for the afternoon rush-hour.

Extra warnings are expected to be in place today, with more traffic wardens and transport marshals. The westbound route will remain open "for the foreseeable future".

Throughout the day, hundreds of passengers were seen abandoning buses approaching Princes Street as they realised the extent of the gridlock.

Police were forced to send extra officers into the area to try to restore order. The problems are thought to have been compounded by the failure of several sets of traffic lights.

The council also chose this week to start a resurfacing programme on the Royal Mile, which closed the Canongate.

George Street, which was used to accommodate traffic rerouted away from Princes Street, was gridlocked with buses at times yesterday.

Lothian Buses admitted that, at the height of the problems, services were taking half an hour to travel from Waverley Bridge to the turn-off from Princes Street on to Hanover Street.

Council officials and tram firm TIE had spent months planning the closure of the junction, to allow a network of underground pipes to be moved.

Willie Gallagher, executive chairman of TIE, said: "I would like to apologise for the delays to bus passengers and drivers as a result of the introduction of the temporary traffic management measures to undertake the utility works around The Mound.

"It was clear by the morning rush-hour that the temporary traffic measures were not fully working.

"Responsive action was taken to improve the immediate traffic congestion and during the day additional improvements have been agreed.

"I would ask all bus passengers and drivers to allow a bit more time in making their journeys."

Lothian Buses admitted the delays had caused havoc to its services across the capital, making a knock-on impact on drivers' schedules.

Sources at the company said the day had been a "nightmare" for drivers and passengers.

"By 8am it was clear the whole thing had turned into a complete disaster. The big problem has been trying to funnel all the bus traffic on to George Street and expecting it to cope with all the other traffic there."

Despite the extent of the problems, the city council declined to comment on how the first day of the tram works had gone.

However, Labour councillor Andrew Burns, the opposition leader, said: "The scale of what's happened this morning strongly suggests to me that the changes just have not been explained, publicised or communicated effectively."

There will be an embargo on tram works in the city centre from December until early January, but more chaos is then expected as Princes Street will be closed to traffic until the festival season starts at the end of July.

The main areas to steer clear of

MOUND: Work to move underground pipes below the main junction at The Mound led to traffic being banned along Princes Street, between Hanover Street and Frederick Street. But westbound access has been restored to Princes Street until the disruption eases.

HAYMARKET: Tram works in the area have led to a series of complex diversions, no-entry signs and one-way systems being introduced. The roadworks are set to last another six months.

CANONGATE: The bottom stretch of the Royal Mile, from St Mary's Street to the Scottish Parliament building, has been closed off for a month to allow major resurfacing work.

GRASSMARKET: Temporary traffic lights have been installed to allow completion of a multi-million-pound revamp before Christmas.

LEITH WALK: Major work to move underground pipes and prepare the way for laying the first tram tracks has led to widespread disruption, with many bus services diverted. The first tracks will be in place by January.