Image source, Getty ImagesImage caption, The USS Connecticut leaves port in 2018.

More than a dozen US sailors have been injured after a nuclear submarine hit an "unknown object" while submerged in waters around the South China Sea.

15 sailors received minor injuries when the USS Connecticut collided with the object on Saturday, US officials said.

The incident comes as tensions mount in the region over Chinese incursions into Taiwan's air defence zone.

Officials said it was unclear what had caused the collision and that the submarine remained operational.

A US Navy spokesperson said it is now headed towards the US territory of Guam.

"USS Connecticut's nuclear propulsion plant and spaces were not affected and remain fully operational," a Navy spokesperson said in a statement. "The extent of damage to the remainder of the submarine is being assessed. The U.S. Navy has not requested assistance."

The USS Connecticut was operating in waters around the South China Sea, where the US and its allies have been carrying out a joint military exercises. The mission includes ships from the US, UK, Japan, Australia, Canada and Holland.

The exercise comes just weeks after the US, UK and Australia agreed a historic security pact in the Asia-Pacific, in what's seen as an effort to counter China. The Aukus pact will see the US share information with Australia to construct its own nuclear powered submarines.

Meanwhile, the US National Security Advisor, Jake Sullivan, said that he was "deeply concerned" about actions that undermine peace across the Taiwan strait. He was speaking after China sent a record number of military jets into Taiwan's air defence zone for the fourth day running.

Asked whether the US was prepared to take military action to defend Taiwan, Mr Sullivan said: "Let me just say this, we are going to take action now to try to prevent that day from ever coming to pass."

On Wednesday, Taiwan's defence minister said that China could be ready to launch a "full-scale" invasion of the island by 2025.