Risk of miscalculations real: Andrews

Australia has urged China and southeast Asian countries squabbling over territory in the South China Sea to sign a code of conduct immediately.

Defence Minister Kevin Andrews issued a veiled swipe at China, during a speech to an Asia Pacific security summit in Singapore on Sunday.

"We are particularly concerned at the prospect of militarisation of artificial structures," Mr Andrews told the summit, a reference to reports China had moved heavy weapons onto contested man-made islands a month ago.

China maintains it has sovereignty over most of the South China Sea, which is a major global shipping route and reportedly has oil and gas reserves.

The Asian giant has ramped up construction of artificial islands building up 2000 acres in recent months, in a move some experts believe is aimed at bolstering its territorial claims.

Vietnam, Malaysia, Philippines, Taiwan and Brunei also claim parts of the sea.

Mr Andrews said Australia was opposed to "coercive or unilateral actions" and hit out at "any large scale land reclamation activity by claimants".

"It is therefore important that countries agree as soon as possible on a substantive code of conduct for the South China Sea between ASEAN members and China," Mr Andrews said.

He called for all parties to exercise restraint, halt reclamation activities, refrain from provocative actions, and ease tensions.

"When tensions are high, the risks of miscalculation resulting in conflict are very real," he said.

A US Navy P-8 Poseidon surveillance aircraft flew above the disputed Spratly Islands last week, which sparked outrage from China.