The first of six batteries of Patriot missiles deployed in Turkey to protect against a spillover of the conflict in neighbouring Syria became operational on Saturday, NATO said.

The battery, provided by The Netherlands, "will help to protect the (southern) city and people of Adana against missile threats," it said in a statement.

"The other five batteries are expected to be in place and operational in the coming days," it added.

As well as another battery from The Netherlands, two German Patriot missile batteries will be positioned in the southeastern province of Kahramanmaras while a further two US batteries will be stationed in Gaziantep, just 50 kilometres (30 miles) north of the border.

Once they are fully deployed, NATO expects the ground-to-air missiles will protect "up to 3.5 million Turks" from a possible Syrian attack or from spillover from the conflict between rebels and Damascus on Turkey's southern border.

The 22-month-old uprising in Syria against President Bashar al-Assad has killed over 60,000 people so far, according to United Nations figures.

NATO, the United States, Germany and The Netherlands agreed in December to deploy the Patriot missiles and up to 350 soldiers each to help fellow NATO member Turkey. The NATO mission is scheduled to last one year.

The US-made Patriot Advanced Capability-3 (PAC-3) missiles are said to be able to take out cruise and ballistic missiles as well as aircraft.

The weapons have already been deployed twice in Turkey. Once during the Gulf War in 1991 and again during the Iraq war in 2003. Ankara again called for the missile deployment after shells fired from Syria landed on the Turkish side of the border late last year, killing several villagers.

Turkish authorities and NATO have stressed that the deployment of the missile system is for defensive purposes only.

The Syrian regime and its ally Russia have criticised the measure.