Gwendolyn Pang, secretary general of the Philippine Red Cross, said 1,000 people may have died in Tacloban, the capital of Leyte province, alone, CNN reported.
"Numbers of undetermined casualties" have been found along roads in the area, said Lt. Jim Aris Alago, information officer for the Navy Central Command.
Officials have already found more than 100 bodies on the streets of Tacloban, a city of about 220,000 residents.
Another 200 people may have died in neighboring Samar province that, like Tacloban, sits along the Leyte Gulf.
Some 100 residents of Tacloban have been reported injured, said Capt. John Andrews, deputy director of the national Civil Aviation Authority.
Rescue crews have been distributing water, medicine, clothing, blankets and ready-to-eat meals, Alago said.
In Cebu province, Dennis Chiong, operations manager for the emergency agency, said communications were totally down in most areas with radio, landline phones and cellphone service all out.
Haiyan is now headed for Vietnam, where officials have been evacuating hundreds of thousands of people from coastal areas, The Wall Street Journal reported.
The storm's winds, which were as high as 195 mph when it hit the Philippines, weakened after it entered the South China Sea, but are still a strong 101 mph, said the Vietnam National Center for Hydro-Meteorology Forecasting.
The typhoon is expected to make landfall about mid-morning Sunday along the country's central coastal provinces.The government said it planned to evacuate some 200,000 people from Danang, a popular tourist destination, by 4 p.m. Saturday.
Dr. Jeff Masters, director of meteorology at Weather Underground, said the region could receive one to two feet of rain.
Haiyan was exceptionally fast-moving, with a forward speed of 25 mph. That spared the Philippines the damage done by sustained heavy rain.