Ten US sailors are missing after a collision between a destroyer and a tanker near Singapore earlier today, the second involving a US warship and a merchant ship in Asia in about two months, triggering a fleet-wide probe of operations and training.
The guided-missile destroyer John S McCain and the tanker Alnic MC collided while the warship was heading to Singapore for a routine port call.
The collision tore a hole in the warship's waterline, flooding compartments that included a crew sleeping area, the US Navy said.
"Initial reports indicate John S McCain sustained damage to her port side aft," it said in a statement. "There are currently ten sailors missing and five injured."
US Defense Secretary James Mattis said Chief of Naval Operations Admiral John Richardson would conduct a broad investigation into US naval operations after the collision.
Richardson said he was calling an "operational pause" worldwide "to make sure that we are taking all appropriate immediate actions to ensure safe and effective operations around the world".
A US Navy official said the pause would involve a staggered day-long stand-down to check safety measures, especially in the Pacific theatre.
In a video statement, Adm Richardson said a comprehensive review would "examine the process by which we train and certify our forces that are forward deployed in Japan to make sure we are doing everything we can to make them ready for operations and war fighting".
He said it would include looking at "operational tempo, trends in personnel, materiel, maintenance and equipment"
He said the review would be conducted on "a very tight timeline" and added: "We need to get to the bottom of this."
The John S McCain's sister ship, the Fitzgerald, almost sank off the coast of Japan after colliding with a Philippine container ship on 17 June.
The bodies of seven US sailors were found in a flooded berthing area after that collision.
The US Navy said last week it had removed the two senior officers and the senior enlisted sailor on the Fitzgerald following an investigation into that collision.
Retired Admiral James Stavridis, a former NATO supreme commander, said it was "shocking" to see two apparently fatal collisions in such a short time.
He said the need for an operational pause and the loss of two front-line ballistic missile defense destroyers for months to come was "deeply worrisome," especially at a time of high tensions with North Korea.
"The Navy has some real soul-searching ahead, and this appears to be a systemic failure of some kind," he said.
Mac Thornberry, the Republican chairman of the US House Armed Services Committee, said the collision involving the John S McCain was the fourth major accident within the US Pacific Fleet this year and highlighted funding cuts and the time crews spent at sea.
"Congress has a duty to provide our sailors with the additional resources they so clearly need, and to do so immediately," he said in a statement.
In May, a South Korean fishing vessel collided with the guided missile cruiser Lake Champlain.
Another guided-missile cruiser, Antietam, damaged its propellers in January while anchoring in Tokyo Bay.
The warship in the latest collision is named for the father and grandfather of US Republican Senator John McCain, who were both admirals.
McCain, the chairman of the Senate Armed Services Committee, is undergoing treatment for brain cancer.
"My thoughts and prayers continue to be with the sailors and families of the USS John McCain and USS Fitzgerald," he said in a statement, in which he called for an investigation that delivered full transparency and accountability.
US President Donald Trump tweeted: "Thoughts & prayers arew/ our @USNavy sailors aboard the #USSJohnSMcCain where search &rescue efforts are underway."
The accidents have come at a tense time.
This month, the John S McCain sailed within 12 nautical miles of an artificial island built by China in the South China Sea, the latest operation to counter what the United States sees as China's efforts to control the waters.
And North Korea last week threatened to fire ballistic missiles towards the US Pacific territory of Guam after US President Donald Trump said he would unleash "fire and fury" if North Korea threatened the United States.
The Navy said significant damage to the John S McCain's hull caused flooding to berthing, machinery, and communications rooms, but the crew was able to stop the flooding and the ship reached Singapore's Changi Naval Base under its own power.
Singaporean, Malaysian and Indonesian ships and aircraft had joined the search for the missing sailors, the US Navy said.
It said the amphibious assault ship America would support the search and provide divers to assess the damage.
Four of those hurt were taken to a hospital in Singapore with non-life threatening injuries. The fifth needed no further treatment.
A crew member on the Alnic MC told Reuters there was no oil spilt from the Liberian-flagged, 183-metre tanker, which was carrying almost 12,000 tonnes of fuel oil from Taiwan to discharge in Singapore.
"We have not discharged the tanker yet," said the crew member, who asked not to be identified.
"We are proceeding to Raffles Reserved Anchorage, where the owners will investigate the matter. There was some damage to the valve but no oil spill."
Stealth Maritime Corporation, the Greece-based owner of the tanker, said it was moving to safe anchorage for assessment.
Reuters later saw the Alnic MC anchored off Singapore.
Singapore's Maritime and Port Authority (MPA) said no injuries were reported on the Alnic, which suffered some damage above the waterline.
"There is no report of oil pollution and traffic in the Singapore Strait is unaffected," the MPA said.
The waterways around Singapore are some of the busiest in the world, carrying about a third of global shipping trade.
Ben Stewart, commercial manager of Maritime Asset Security and Training in Singapore, said early indications suggested thewarship may have turned across the front of the tanker.
"Instances like this should be rare and they are rare," Mr Stewart said.
The Fitzgerald and John S McCain, built in the same shipyard, are both ballistic missile defence (BMD) capable ships and part of the same Japan-based destroyer squadron.
The Seventh Fleet has six ships assigned to BMD patrols, with half on patrol at any time.