MEXICO CITY, JULY 30 -- At least 33 persons were killed today when a cargo plane slammed into a busy highway outside Mexico City in the evening rush hour, plowing into cars, houses and a gasoline station, Red Cross officials said.

Radio stations said the death toll may be as high as 50.

A Mexico City airport official said the plane belonging to the airline AeroCaribe of neighboring Belize, was on its way to Miami and was believed to be carrying four crewmen, four passengers and 18 horses belonging to the Mexican equestrian team for the forthcoming Pan-American games in Indianapolis. But one Mexican radio station quoted a Mexican team official as denying this.

Reporters who reached the scene shortly after the crash said most of the dead appeared to have burned to death in their cars, a roadside house and a restaurant.

They said the plane, which had taken off from Mexico City airport minutes earlier, apparently crashed in a lightning and rainstorm shortly after 5 p.m. local time (7 p.m. EDT) on one of the country's busiest highways.

Witnesses said a nearby gasoline station caught fire.

The plane had started out in Belize, picked up the horses at Mexico City International Airport and took off in a heavy rainstorm, airport officials said. It was headed for Miami and then for Indianapolis, they added.

Airport officials said the plane, a four-engine propeller-driven Boeing 377, crashed 10 miles outside the capital on the main highway to the city of Toluca.

"I remember seeing lightning. The plane's engines seemed to fail and I saw it skim over the trees, chopping off tree tops," said Miguel Parra, 26, who lives 500 yards from the crash site.

"It cleared an overpass over the highway, hit some high tension wires and exploded," said Parra, himself covered in blood after aiding rescuers.

He said he saw what he thought were the pilot and copilot emerge, burned but not badly hurt, from the wreckage. There was no immediate confirmation of this.

A spokesman for the ABC hospital said later that the pilot and copilot survived. She said she did not know their nationalities but named them as pilot Frederick Moore and copilot Robert Banty.

She said a third foreign survivor was Brian Stuart, but she did not know his nationality.

{In Washington, a State Department spokeswoman said that the pilot and three other crew members were U.S. citizen and had survived. She could not give their names.}

Reporters at the scene said most of the dead appeared to have been in the two-story roadside house in which several families lived. At least 26 cars littered the highway.

The twisting highway is the western continuation of Mexico city's central Reforma Avenue. It was completely blocked after the crash, causing traffic chaos in the capital.

The plane was barely recognizable, a burned-out hulk on the side of the highway.

Reporters at the scene saw several dead horses, and residents said they had seen what they believed were policemen killing the most seriously injured horses.

One reporter saw a horse, which appeared to be a thoroughbred racehorse or showjumper, being led away alive.

Red Cross officials at the crash scene said they had counted at least 33 bodies. Many burned victims were rushed by ambulance or helicopter to the Red Cross hospital in the residential Polanco district.