Oman authorities have raised the alert level to orange as the sultanate has started receiving heavy rains on the east coast, triggered by the advancing tropical cyclone Phet.

The cyclone was expected to make landfall late on Thursday at the earliest before barrelling toward the oil-exporting Gulf Arab state's LNG facilities.

But Phet, a Category 4 storm with winds of over 130 mph (210 kph), would weaken substantially before brushing Oman's sparsely populated southeast coastline, according to storm risk forecasts shown on website www.tropicalstormrisk.com.

"It will hit the land at the eastern region by first entering Masirah (Island) around 2200 (local time) tonight," Ahmed Al Harthy, a senior Omani meteorological official told Reuters. "The storm will be felt, though less severe, all the way to Muscat on Friday."

Oman state television said the government had ordered police and the air force to evacuate people from areas of eastern Oman, where waves were 8 metres (26 feet) high. Al Arabiya television said Oman had raised its storm alert on Thursday.

National carrier Oman Air said it had cancelled two flights so that aircraft could evacuate people from Masirah island, home to several villages and an Omani air force base.

"Hundreds of people have been evacuated, most of them from the Masirah Island," an Oman civil defence department spokesman said, adding that some of the evacuees had been taken to Muscat.

"There are many more who refused to budge."

Phet was due to hit Masirah as a Category 3 cyclone but would weaken to Category 2 before hitting Oman's mainland. It would then re-emerge over the north Indian Ocean as a tropical storm and march on toward Pakistan, Tropical Storm Risk said.

Pakistani authorities had already evacuated nearly 1,000 people and were on standby for more. In a worst-case scenario, up to 50,000 people could be affected on Pakistan's coast, said Commander Salman Ali, a spokesman for Pakistan Navy in Karachi.

Phet initially had been forecast to become a Category 5 storm, the most powerful category with winds of over 156 mph.

The cyclone would steer east of the Gulf and the Strait of Hormuz, used by ships carrying 17 million barrels per day (bpd) of oil, 40 percent of all seaborne oil, and may disrupt shipping moving from the Gulf toward the Indian Ocean.

Most Omani oil exports move from Mina al-Fahal port near the capital Muscat. Operations at Oman LNG, the liquefied natural gas export facility, were so far unaffected, Nasser al-Kindy, head of Oman LNG corporate communications, told Reuters.

"Today, everything is okay. Oman LNG is still (in) business, production is not affected. We are monitoring the situation," Kindy said.

The three LNG production facilities, known as trains, are in Sur in the east, close to the path of the storm. They produce about 8 million tonnes of LNG per year.

The east is also home to Oman's protected green back turtle.

A previous cyclone in 2007 killed at least 54 people in Oman and Iran. – Reuters