Chinese dredging vessels are purportedly seen in the waters around Fiery Cross Reef in the disputed Spratly Islands in the South China Sea in this still image from video taken by a P-8A Poseidon surveillance aircraft provided by the United States Navy May 21, 2015. Reuters China’s rapid claim on contested islands in the South China Sea is beyond anything seen previously and raises legitimate questions about Beijing’s intentions in the region, the secretary of the Australian defence department, Dennis Richardson, said.

Richardson told a Senate estimates committee on Monday that the military buildup on China’s reclamation program in the South China Sea “dwarfs” what other nations in the region have done previously.

“The land reclamation activity by China in the South China Sea has been at a pace and scale in the last two years beyond anything we have previously seen. It dwarfs what the other claimant states have done, and the size of the land reclamation does raise questions about its purpose,” Richardson said.

China has reportedly started building up its military presence in the artificially created islands, in a region believed to be rich in oil and gas reserves.Several countries have laid claim to the islands, situated just north of Brunei, and the naval corridor is an important shipping route for Australian vessels.

Labor has also raised concerns over mounting tension in the South China Sea and has urged the government to tread carefully.

The shadow foreign minister, Tanya Plibersek, told ABC radio: “Australia and our Asian neighbours in particular and others in the region have an expectation of being able to move freely now and in the future in this area.”

She urged the government to take a softly-softly approach to China’s land reclamation program.

“It’s important that we continue to see freedom of movement in that area, particularly freedom of shipping, but making sure that we use language that calms the situation rather than inflames it is very important,” Plibersek said.

“Our contributions should be to ensure that tensions are de-escalated and understandings between the parties continue to improve.”

Plibersek’s comments followed those made by the defence minister, Kevin Andrews, who has voiced opposition to any move by China to militarise the disputed islands.

The aircraft carrier USS Nimitz (CVN 68), the guided-missile cruiser USS Chosin (CG 65), the guided-missile destroyers USS Sampson (DDG 102) and USS Pinkney (DDG 91), and the guided-missile frigate USS Rentz (FFG 46) operate in formation in the South China Sea. US Navy Andrews hit out at Beijing’s reclamation program during an Asian security summit in Singapore on Sunday.

“We remain concerned by any developments in the South and East China Sea which raise tensions in the region,” he told the summit. “Australia has made clear its opposition to any coercive or unilateral actions to change the status quo in the South and East China Sea. This includes any large-scale land reclamation activity by claimants in the South China Sea.

“We are particularly concerned at the prospect of militarisation of artificial structures,” he continued.

Andrews urged all the parties involved in the dispute – which include China, Malaysia, Brunei, Vietnam, Taiwan and the Philippines – to sign a code of conduct immediately, in a bid to ease tensions.

“Disputes must be resolved peacefully and Australia urges all parties to exercise restraint, halt all reclamation activities, refrain from provocative actions and take steps to ease tensions,” Andrews said. “Because when tensions are high, the risks of miscalculation resulting in conflict are very real.”

The opposition leader, Bill Shorten, echoed the defence minister’s call for multilateral cooperation.

“The only path to working out all these issues … is through international negotiation and discussion. There’s no other path to long-term peace than that,” Shorten said. “We’re all in this together.”

Labor has asked the Coalition for a briefing on the situation in the disputed region.

This article originally appeared on guardian.co.uk