(Adds Ukrainian official on other troop movements, background)

SEVASTOPOL, Ukraine, March 14 (Reuters) - A Russian warship unloaded trucks, troops and at least one armoured personnel carrier at a bay near Sevastopol in Crimea on Friday morning, as Moscow continued to build up its forces on the Ukrainian peninsula.

A Reuters journalist saw trucks driving off the Yamal 156, a large landing ship, at Kazachaya Bay near Sevastopol. One flatbed truck was carrying an armoured personnel carrier (APC).

The vehicles drove off a landing ramp on to a low shoreline of open ground near an oil storage terminal from the ship, which is capable of carrying over 300 troops and up to a dozen APCs.

On Monday, a Reuters journalist saw a column of at least 100 Russian vehicles, including trucks, APCs and artillery on a road in the same area. It is Ukrainian territory, some 15 km (10 miles) from the port at Sevastopol which Moscow leases from Kiev to station its Black Sea Fleet.

Crimea's pro-Russian authorities have denied there are any Russian troops on the peninsula outside the Sevastopol base, even though masked gunmen surrounding Ukrainian military installations drive vehicles with Russian licence plates and identify themselves to Ukrainian soldiers as Russian troops.

Ukraine's border guards said they captured a Russian soldier driving to the mainland from Crimea on Friday with a uniform, military papers and rifle in his car. The man said he was lost.

Crimeans vote on Sunday whether to become part of Russia or to choose greater autonomy within Ukraine, a step that pro-Moscow officials say is a stepping stone to joining Russia.

Ukrainian officials and analysts estimate that some 20,000 Russian troops are in Crimea, of whom fewer than 12,000 are attached to the Black Sea Fleet, with the remainder comprising infantry and paratroopers brought from Russia. Under the terms of the lease for the fleet, Moscow can station up to 25,000 troops in Sevastopol, but not on other Ukrainian territory.

A Ukrainian defence ministry official in Crimea said on Friday that witnesses in Kerch, a port at the eastern end of the peninsula, saw Russian armoured vehicles landed. Vladislav Seleznyov wrote on Facebook that a train carrying 14 S-300 surface-to-air missile launchers was at the railway station.

He said another source reported a column of about 100 vehicles, including trucks and armoured personnel carriers, was heading from the northern town of Dzhankoi toward Perekop, on an isthmus leading to mainland Ukraine. (Additional reportng by Pavel Polityuk in Kiev; Writing by Andrew Osborn and Alastair Macdonald)