The US Defence Intelligence spy agency has had to apologise over an acerbic tweet which fuelled a heated incident between US and Chinese officials.

Barack Obama played down the spat and warned against "over-cranking" the situation after he landed in Hangzhou on the eve of the G20 summit only to find there was no red carpet and he had to leave by a different plane exit in what appeared to be a deliberate snub.

This was followed by shouting matches between Chinese officials and Secret Service agents when Obama met with Chinese President Xi Jinping over US journalists' access to Obama, which Chinese officials unexpectedly limited, CNN reported.

After the rows, the Pentagon's Defence Intelligence Agency tweeted: "Classy as always China." But hours later the agency apologised, said the tweet had been posted by mistake and removed it

China-US confrrontation

Asked about the airport meltdown, Obama conceded that "the seams are showing a little more than usual" in the "jostling that takes place behind the scenes."

But he added: "I wouldn't over-crank the significance of it, because, as I said, this is not the first time that these things happened.

"And it doesn't just happen here," he said, meaning China. "It happens in a lot of places, including, by the way, sometimes, our allies. We've got a lot of planes and a lot of helicopters and a lot of cars and a lot of guys, and if you're a host country, sometimes it may feel a little bit much."

The first confrontation occurred at Hangzhou Xiaoshan International Airport when US journalists travelling with Obama were ordered away from the president's Air Force One by Chinese officials. When America officials said the journalists were staying put, a Chinese aide said angrily: "This is our country. This is our airport."

Later at the West Lake State House where Obama and Xi met, White House aides, protocol officers and Secret Service agents argued heatedly for 15 minutes with Chinese officials over how many US journalists would be allowed in.

"Calm down, please. Calm down," a White House official said. A foreign ministry official was overheard to say in Chinese: "Stop, please. There are reporters here."

There was yet another confrontation about which journalists would be allowed inside during the meeting with Obama, Xi and United Nations Secretary General Ban Ki-moon. Chinese authorities only allowed two reporters, despite protestations from the Americans.