A first shipment of material has been removed from Syria under a deal to rid the country of its chemical weapons arsenal, the joint mission overseeing the disarmament said Tuesday.

"A first quantity of priority chemical materials was moved from two sites to the port of Latakia for verification and was then loaded onto a Danish commercial vessel today," the mission said in a statement.

It added that the ship had sailed for international waters and would remain at sea "awaiting the arrival of additional priority chemical materials at the port".

"This movement initiates the process of transfer of chemical materials from the Syrian Arab Republic to locations outside its territory for destruction," the statement said.

Maritime security is being provided by naval escorts from China, Denmark, Norway and Russia, it added.

The head of the disarmament mission, Sigrid Kaag, was on Wednesday to brief the United Nations Security Council on the latest progress in the operation.

The removal had been scheduled to take place before December 31, but Syria's worsening civil war, logistical problems and bad weather had delayed the operation.

The year-end deadline for the removal of key weapons components was the first major milestone under a UN Security Council-backed deal arranged by Russia and the United States that aims to eliminate all of Syria's chemical arms by the middle of this year.

Under the plan, the chemicals will be taken from Latakia to a port in Italy where they will be transferred to a US Navy vessel fitted with equipment to destroy them at sea.

The OPCW has turned to the US military for assistance after no country volunteered to destroy the chemical weapons on its soil, despite an international consensus that the weapons be neutralised outside Syria.

The US-Russia deal was aimed at heading off US military strikes against President Bashar al-Assad's regime after hundreds of people were killed last August in a chemical weapons attack outside Damascus.