A powerful typhoon that caused massive destruction and scores of deaths in the Philippines is now churning towards Vietnam.

Weather forecasters say Typhoon Haiyan could make landfall in the country on Sunday.

Vietnamese authorities have evacuated several hundred thousand people from coastal areas, where the storm's outer bands are already causing high winds and rough seas.

In the Philippines, Typhoon Haiyan made landfall as one of the most powerful storms on record, with maximum sustained winds of about 300 kilometers an hour.

Officials say 138 people are confirmed dead, but the Philippine Red Cross says the actual death toll may be more than 1,200. Rescuers are sifting through rubble to try to reach victims.

Relief workers estimated that many of the dead are on the hard-hit island of Leyte.

Philippine interior secretary Mar Roxas says it is difficult to describe the extent of damage in Leyte's capital, Tacloban.

"The devastation is - I do not have the words for it. It is really horrific. It is a great human tragedy. There is no power. There is no light."

U.N. emergency relief coordinator Valerie Amos said a U.N. disaster and assessment team has been deployed to Tacloban.

Separately, U.N. Secretary General Ban Ki-moon offered his condolences to the Philippines, saying he was deeply saddened by the "extensive loss of life."

A U.S. relief team has been deployed to the region. The U.S. Agency for International Development says the team will conduct damage assessments, track conditions and "advise on additional needs."

The U.S. has also made $100,000 available for relief supplies.

Typhoon Haiyan weakened after crossing the Philippines but regained some strength as it began moving westward over the South China Sea toward Vietnam.