(Adds details of injured couple in paragraph 6)

BEIJING, Feb 25 (Reuters) - Three people set themselves on fire in the heart of downtown Beijing on Wednesday, state media and a witness said, and city police said they appeared to have come to the capital to voice "personal complaints".

The trio set off the blaze in their car just before 3 p.m. (0700 GMT) at the intersection of the city's main Chang'an thoroughfare and high-end shopping street, Wangfujing.

A witness saw "some kind of incendiary device" explode when police wrenched open the door of a small silvery-grey car, with three large Chinese flags attached to its roof.

The Beijing Municipal Public Security Bureau said in a faxed statement that the passengers were in a car with non-Beijing plates and were stopped by police who thought the car looked odd. It did not describe the incident as self-immolation.

"When they were advancing to examine it, the inside of the car caught fire and it was swiftly extinguished," said the statement. Two of the passengers were hospitalized.

The man, 59, is seriously burnt with injuries to his throat and head, the Xinhua news agency said late on Wednesday. The woman, 58, may have to have some fingers amputated.

"Based on initial inquiries, the three came to Beijing to voice personal grievances," said the police statement.

China's national parliament begins its annual session next week and many aggrieved citizens try to come to the capital at this time to air complaints about corruption, lost land and jobs and investments gone sour.

The statement made no suggestion that the passengers were Tibetan or Uighur, two minorities often treated as security risks by authorities. Wednesday marks Tibetan New Year and Beijing tightened security in Tibetan areas to prevent unrest.

A man was pulled from the car and his apparently limp body was later seen laid out on the street, the witness said, while other officers pulled the screaming woman from the passenger door of the partially smouldering vehicle.

Police also removed piles of blankets and cans from the back seat of the car, said the witness, who was cycling by.

Photos released by a blogger showed at least one body lying on the street.

In 2001, five people, who the government said belonged to the banned spiritual movement Falun Gong, set themselves on fire on Tiananmen Square, the symbolic political heart of China about 1 km (half a mile) to the west of Wednesday's fire. Falun Gong denied the five were members of the group.

In 2006, a man also set himself on fire there to protest not being paid, media said, but as a magnet for protest the square has very high security. (Reporting by Emma Graham-Harrison, Chris Buckley, Benjamin Kang Lim, Ian Ransom and Lucy Hornby; Editing by Louise Ireland)

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