SINGAPORE >> Ten U.S. sailors are missing after a collision between the USS John S. McCain and a tanker early Monday east of Singapore, the second accident involving a ship from the Navy’s 7th Fleet in the Pacific in two months.

The Navy said five sailors were hurt in the collision between the guided-missile destroyer and the 183-meter (600-foot) Alnic MC, an oil and chemical tanker. Four of them were evacuated by a Singaporean navy helicopter to a hospital in the city-state for treatment of non-life threatening injuries, and one did not require further medical attention.

The McCain 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.

The destroyer was damaged on its port side aft, or left rear, from the collision that happened at 5:24 a.m., the Navy’s 7th Fleet said, but was heading to port under its own power. The Singapore government said no crew were injured on the Liberian-flagged Alnic, which sustained damage to a compartment at the front of the ship some 7 meters (23 feet) above its waterline.

Singapore sent tugboats and naval and coast guard vessels for the search and rescue effort. Malaysia’s navy chief Ahmad Kamarulzaman Ahmad Badaruddin tweeted that two ships as well as aircraft from its navy and air force were helping with the search for the missing sailors. He tweeted a photo of the McCain that showed a gaping hole in its side near the waterline. The Navy said Osprey aircraft and Seahawk helicopters from the USS America were assisting in the search.

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

The collision was the second involving a ship from the Navy’s 7th Fleet in the Pacific in two months. Seven sailors died in June when the USS Fitzgerald and a container ship collided in waters off Japan.

The Fitzgerald’s captain was relieved of command and other sailors were being punished after the Navy 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.

President Donald Trump has expressed concern for the McCain’s crew.

Trump returned to Washington tonight from his New Jersey golf club. When reporters shouted questions to him about the McCain, he responded, “That’s too bad.”

About two hours later, Trump tweeted that “thoughts and prayers” are with the McCain’s sailors as search and rescue efforts continue.

The 154-meter (505-foot) McCain is named after U.S. Sen. John McCain’s father and grandfather, who were both U.S. admirals. It’s based at the 7th Fleet’s homeport 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.

McCain said on Twitter that he and his wife, Cindy, are “keeping America’s sailors aboard the USS John S McCain in our prayers tonight — appreciate the work of search & rescue crews.”