At least 10 U.S. sailors are missing after USS John S. McCain collided with a tanker early Monday east of Singapore, the second accident involving a ship from the navy's 7th Fleet in two months.

The U.S. navy said five other sailors were hurt in the collision between the guided-missile destroyer and the 183-metre Alnic MC, an oil and chemical tanker. Four of them were evacuated by a Singaporean navy helicopter to a Singapore hospital for treatment of non-life threatening injuries and one did not require further medical attention.

The warship had been heading to Singapore on a routine port visit after conducting a sensitive freedom of navigation operation last week by sailing near one of China's man-made islands in the South China Sea.

It wasn't immediately clear if the Liberian-flagged Alnic sustained damage or casualties.

The McCain was damaged on its port side aft, or left rear, from the collision that happened at 5:24 a.m. local time, the navy's 7th Fleet said, but arrived at Changi Naval Base in Singapore after suffering damage to its hull that caused flooding in compartments, the navy said.

"Significant damage to the hull resulted in flooding to nearby compartments, including crew berthing, machinery, and communications rooms. Damage control efforts by the crew halted further flooding," the U.S. 7th Fleet said in a statement.

Ahmad Kamarulzaman Ahmad Badaruddin, Malaysia's navy chief, tweeted that two ships as well as aircraft from its navy and air force have been deployed to help look for the missing U.S. sailors.

USA-NAVY/CRASH

Tanker Alnic MC is seen in Singapore waters after a collision with USS John S. McCain. (Christoph Van Der Perre/Reuters)

The navy said Osprey aircraft and Seahawk helicopters from USS America were assisting in the search. It also said tugboats and Singaporean naval and coast guard vessels were in the area to render assistance.

There was no immediate explanation for the collision and the navy said an investigation would be conducted. Singapore, a city-state at the southernmost tip of Malaysia, is one of the world's busiest ports and a U.S. ally, with its naval base regularly visited by American warships.

The collision is the second involving a ship from the U.S. navy's 7th Fleet in the Pacific in two months. Seven sailors died in June when USS Fitzgerald and a container ship hit each other in waters off Japan. 

The Fitzgerald's captain was relieved of command and other sailors were being punished after investigators found poor seamanship and flaws in keeping watch contributed to the collision, the navy announced last week. An investigation into how and why the Fitzgerald collided with the other ship was not finished, but enough details were known to take those actions, the navy said.

Two other U.S. warships were involved in smaller accidents in the western Pacific earlier this year. USS Antietam was damaged after it ran aground off the coast of Japan on Jan. 31, while USS Lake Champlain struck a South Korean fishing boat on May 9. 

U.S. President Donald Trump has expressed concern for the McCain's crew and late Sunday tweeted that "thoughts and prayers" are with the sailors. 

The 154-metre McCain, named after U.S. Senator John McCain's father and grandfather, who were both U.S. admirals, is based at the 7th Fleet's home port of Yokosuka, Japan. It was commissioned in 1994 and has a crew of 23 officers, 24 chief petty officers and 291 enlisted sailors, according the navy's website.

With files from Reuters