There were differing theories about the cause of the blast — which did not cause any serious injuries or an oil spill — ranging from a terrorist attack to an explosion of gases.
Port officials in the neighbouring United Arab Emirates even said the ship was hit by a tremor-triggered wave.
On Wednesday afternoon, the M.Star of the Mitsui OSK Lines, was steaming under its own power to the United Arab Emirates for repair.
Japan’s transport ministry suspected an attack on the tanker.
“Since one of the crew saw a flash on the horizon immediately before the blast, the company suspects it was highly likely an attack,” the ministry said, adding that the immediate area was not known for piracy.
It said one crew member was injured and the ship was partly damaged but able to keep sailing after the blast hit at 12:30 am (2030 GMT Tuesday).
And Junto Endoh, general manager in the Doha liaison office for Mitsui OSK Lines, told Dow Jones Newswires, the explosion was “maybe an attack, not a spontaneous accident; it may be a terrorist attack.”
The vessel — crewed by 16 Filipinos and 15 Indians — was carrying 270,000 tonnes of crude oil but did not suffer a spill.
It was heading from the UAE to the Japanese port of Chiba at the time of the blast, but turned back for inspection, a company executive said.
The US Navy Fifth Fleet, based in Bahrain, said the vital shipping route, through which passes an estimated 40 percent of oil exports remained open.
“The Strait of Hormuz remains open for safe navigation and shipping lanes are unaffected by this incident,” a statement said.
“The cause of the explosion and extent of damage is currently unknown.”
“Initial damage assessment from the ship’s owner, Mitsui OSK Lines Ltd., Japan, is that one life boat was blown off the ship and there is some damage to the starboard hatches.”
The US Navy offered to help but the crew determined it was not needed, the statement said, adding the ship was heading to the port of Fujairah, in the UAE, “under their own power to make repairs.”
The ship is expected to arrive in Fujairah, on the east coast of the UAE around 5:00 pm (1300 GMT), port director Captain Mussa Murad said.
In Iran, Ali Akbar Safai, head of shipping in Hormozgan province on the Gulf, told Fars news agency a “fire was caused by a blast on the deck of this vessel” adding that it was “controlled by the forces present in the region and the crew.”
Mohammad Hakimi, another Iranian shipping official, told Mehr news agency “the blast on the Japanese ship happened in Omani waters.”
And Attollah Sadr, head of Iran Shipping and Ports Organisation, ruled out a terrorist attack. “Because of inflammable gases and vapours in oil tankers, a blast is likely,” he told Mehr.
Eiko Mizuno, a Mitsui spokeswoman in Tokyo, told AFP: “The crew member was not seriously injured. His arm was cut by shattered glass.
“The ship is now sailing to the port without having to be towed. It is expected to reach the port as early as late Wednesday (local time).”
“The damage did not spark a fire of the oil inside the tanker. Further details have yet to become available as a full investigation will be launched once the tanker gets to the port.”
The Strait of Hormuz, less than 100 kilometres (60 miles) at its widest point, separates Oman from Iran and is the gateway into the oil-rich Gulf.
Regional tensions are high as Western powers pressure Iran to abandon its nuclear ambitions, suspecting the regime is seeking a nuclear bomb. Fresh UN sanctions were adopted last month.
And pirates based in lawless Somalia have staged scores of attacks in waters off the Horn of Africa, deep into the Indian Ocean, and as far north as the coastal waters of Oman in recent years.
