A "ring of steel" is in place around the conference centres

Police have introduced extra security measures around the G-Mex Centre and nearby hotels, with traffic restrictions on surrounding streets.

The road closures caused some problems for motorists trying to get into the city along Oxford Road on Friday.

It is the first time the conference has been held in Manchester since 1917.

'Ring of steel'

The security operation for the conference will be the biggest ever mounted by Greater Manchester Police (GMP), costing �4.2m and involving 1,000 officers every day.

Security arrangements had to be reviewed earlier in the week after thieves stole a laptop containing confidential plans for the conference.

In addition to GMP, officers from the security services, the military, Special Branch and Greater Manchester's Anti-Terrorist Unit are involved in the operation.

The level of inconvenience caused to local people going about their daily business is horrendous and totally unacceptable Councillor Paul Shannon Liberal Democrats

Metal fencing, heavy concrete blocks and security check points have all been installed to create a "ring of steel" around the G-Mex and the Manchester International Convention Centre.

Work has also taken place to make the "buffer zone" outside the security barriers secure.

Ch Supt Bryan Lawton, said: "Whilst this is obviously a large security operation, we are doing everything possible to minimise disruption to people using the city centre.

"People will see a highly visible police presence, but we hope this will reassure."

But the city centre security arrangements were criticised by the deputy leader of Manchester's Liberal Democrats, Councillor Paul Shannon.

He said he counted "43 buses jammed nose to tail" down Oxford Road towards the university after Peter Street was closed from Deansgate to Portland Street.

"The level of inconvenience caused to local people going about their daily business is horrendous and totally unacceptable," he said.

'World watching'

But a spokeswoman for Greater Manchester Police said there had been no "major traffic problems" on Friday.

Nevertheless, police are urging motorists to avoid coming into the city centre where possible and park at sites near the inner-ring road.

Thousands more visitors are expected in the city on Saturday to take part in a Stop The War Coalition march, which starts at 1300 BST.

Spokeswoman Lindsay German said she expected the rally to be even bigger than the estimated 30,000.

Steve Mycio, of Manchester City Council, said: "We want everyone to be prepared for a busy city and to plan your journeys in advance.

"The eyes of the world will be on Manchester when this conference is taking place."