A Chinese military aircraft had an “unsafe” encounter with a US Navy surveillance aircraft near a contested reef in the South China Sea, the US Pacific Command said Friday.

The two planes came within 1,000 feet (300 metres) of each other during Wednesday's incident near the Scarborough Shoal, which is claimed by both the Philippines and China, according to Pentagon spokesman Jeff Davis.

The close encounter comes amid heightened tensions between the United States and China over Beijing's moves to establish a presence in disputed areas of the South China Sea by building reefs and atolls into artificial islands.

“An interaction characterised by US Pacific Command as 'unsafe' occurred in international airspace above the South China Sea between a Chinese KJ-200 aircraft and a US Navy P-3C aircraft,” said US Pacific Command spokesman Rob Shuford.

“The US Navy P-3C was on a routine mission operating in accordance with international law.” Davis said the Chinese aircraft essentially “crossed the nose” of the American plane, causing it to “make an immediate turn.” “We don't see any evidence that it was intentional,” the spokesman said, adding that the incident appeared to be a “one-off” encounter.

“Clearly we have our disagreements with China over militarisation of South China Sea,” he said, adding that interactions between ships and planes are “largely professional and safe.” The KJ-200 is an airborne early warning and command plane, while the P-3 is a maritime surveillance aircraft.

The Pacific Command said it would address the issue “in appropriate diplomatic and military channels.” - China responded 'legally and professionally' -

A Chinese defense ministry official told The Global Times that the Chinese pilot had responded “legally and professionally” to the US plane when it approached the aircraft.

“We hope that the US could take the bilateral military relations into consideration and adopt practical measures to eliminate the root cause of air and sea mishaps between the two countries,” the official said on condition of anonymity.

China asserts sovereignty over almost all of the resource-rich region despite rival claims from Southeast Asian neighbors and has rapidly built reefs into artificial islands capable of hosting military planes.

US President Donald Trump's administration so far has taken a tough stance on China's claims in the South China Sea, insisting it will defend international interests there.

During his confirmation hearings, new US Secretary of State Rex Tillerson raised the threat of blocking China's access to the contested islands.

Under president Barack Obama's administration, Washington insisted it was neutral on the question of sovereignty over the South China Sea islets, reefs and shoals, calling for the disputes to be resolved under international law.

But the US has dispatched aircraft and naval patrols to assert its rights of passage through international spaces.