A woman has been killed and five others injured after a tree fell on a wedding party in California.

A four-year-old girl was said to be in a critical condition with head injuries after the large eucalyptus fell unexpectedly, trapping several people who had gathered under the tree to take pictures.

The rest of the injured suffered minor injuries and were taken to nearby hospitals after the incident at Whittier's Penn Park, according to Los Angeles County Fire Department Inspector Joey Marron.

Officials said there had been no warnings that trees in the area could have been vulnerable to falling.

Some said the tree might have been weakened by years of fluctuating drought and heavy rainfall.

One witness said the tree split in two and landed on several people.

Another said a similar tree fell in the area last year.