The world's chemical watchdog solicited private companies on Thursday to help with the destruction of around two-thirds of Syria's vast stock of chemical weapons, as options dwindle ahead of a tight deadline to complete the task.

The Organisation for the Prohibition of Chemical Weapons (OPCW) published a note on its website saying it wanted to identify companies for disposing of chemicals and other materials "associated with the destruction of Syrian chemical weapons."

It requested companies "interested in participating in a potential tendering process" to approach the OPCW.

The world is in agreement about destroying Syria's chemical weapons as part of a US-Russia deal aimed at heading off strikes on the Damascus regime after deadly chemical attacks in August.

But despite consensus on destroying the chemicals outside war-wracked Syria, no country has volunteered to have them destroyed on its soil.

Syria is cooperating with the disarmament and has already said it had 1,290 tonnes of chemical weapons and precursors, or ingredients, as well as over 1,000 unfilled chemical munitions, such as shells, rockets or mortars.

Some chemical weapons are destroyed through a process known as hydrolysis, in which agents, like detergents, are used to neutralise chemicals such as mustard gas and sulphur, resulting in liquid waste known as effluent.

Nerve gases such as sarin are often better destroyed through incineration.

The OPCW request said 798 tonnes of chemicals needed to be disposed of, as well as 7.7 million litres of effluent.

"These are chemical products that can be destroyed in a secure way by the industrial sector (including) some of the most toxic chemicals that have not yet been mixed," OPCW spokesman Christian Chartier told AFP.

"This is about two-thirds of Syria's chemical weapons," he said.

"Businesses will be chosen as with any tender, according to criteria including the proposed timeframe, competence, price, etc," Chartier said.

The OPCW's appeal would nevertheless require for a country to accept for the chemicals to be received on its soil, a solution that has so far proved elusive.

Any company that might receive the chemicals would need to complete their destruction by the same mid-2014 deadline.

The document said that the deadline for destruction of resulting effluent would be December 31, 2014, or six months after the UN Security Council-backed deadline for Syria to completely destroy its arsenal.

Destruction by companies would be monitored by the OPCW, which must confirm their total and safe destruction.

Companies have just a week, until November 29, to express their interest, the OPCW said.

With the number of potential hosts dwindling, the OPCW said Wednesday the chemicals could even be destroyed at sea on floating incinerators.

The OPCW's Executive Council on November 15 approved a final roadmap for ridding Syria of its arsenal by mid-2014 to be approved by December 17.

A team of UN-OPCW inspectors has been on the ground since October checking Syria's weapons and facilities.

Destruction of declared chemical weapons production facilities was completed last month and all chemicals and precursors placed under seal, the OPCW said last month.

Belgium said on Monday that it was not favourable to destroying Syria's weapons on its soil, and last week Albania also rejected the proposal.

Norway too has ruled out destroying the chemical weapons on its soil but along with Denmark has offered ships to help take the chemicals out of Syria.

France said on Tuesday that it was prepared to offer expertise, but denied that it had been approached to destroy the chemicals.