A spokesman for the Georgian Defence Ministry, which is loyal to Mr Shevardnadze, said that Samtredia, a key rail and road junction between the Black Sea coast and the capital, Tbilisi, fell after the last government forces retreated towards the east with rebels in pursuit.
Mr Shevardnadze, the former Soviet foreign minister, suffered the added indignity of seeing the rebels seize the smaller town of Khoni, north of Samtredia, after earlier being repulsed by government troops.
'I call on all units to unite under the Defence Ministry and let us fight together for the welfare of Georgia,' said the National Guard commander, Jemal Chumburidze, on Georgian television. He said the fragmentation and disorganisation of government troops were to blame for the rebels' success, and added: 'We must . . . save Georgia.'
The Interior Ministry said dozens of civilians and soldiers had died in the battle for Samtredia, which began when rebels backed by tanks and artillery crossed the river Tskhenistskali at dawn. Resistance soon crumbled and the rebels reached the centre within hours. Government troops fled towards Kutaisi, Georgia's second city. Some were surrounded by Mr Gamsakhurdia's men.
There was no independent word from Samtredia on casualties and there were no details of rebel losses.
The fall of Samtredia will drastically cut the level of supplies reaching Tbilisi from Batumi, the only Black Sea port still in government hands. The landlocked former Soviet republic of Armenia, to the south-east, could also suffer because it relies on supplies of grain and other goods from Batumi.
Mr Gamsakhurdia, the former Georgian president, is a dissident from the Soviet period elected after independence but deposed in January 1992 amid charges of dictatorship. He has made clear his intention of ousting Mr Shevardnadze. Since his return from exile last month, his troops have captured large swaths of Mingrelia in western Georgia, his traditional stronghold and home region.
He has taken advantage of Mr Shevardnadze's humiliation last month, when the Georgian president pledged to defend 'to the end' the Black Sea province of Abkhazia from separatist rebels, but then had to flee as Russian-backed Abkhazian forces routed his troops. Georgia has been completely destabilised by the Abkhazian war, combined with national conflicts in Ossetia, and now civil war.Reuse content