By Thanarith Satrusayang and Amy Sawitta Lefevre
BANGKOK (Reuters) - A huge crowd of Thais gathered on Saturday outside Bangkok's Grand Palace to sing the royal anthem in honor of King Bhumibol Adulyadej, who died on Oct. 13 after seven decades on the throne.
The government has declared a year of mourning for the 88-year old king, who was seen as a father figure for generations of people, and, though a constitutional monarch, a calming influence over the country's often turbulent politics.
People dressed in black traveled by bus, boat and on foot to Sanam Luang, a tree-lined open space that has been used for royal cremations outside the river-side Grand Palace, bringing the area to gridlock well before the singing.
Police said more than 150,000 were in Sanam Luang and side streets with more people expected through the day.
The royal anthem, known as Sansoen Phra Barami, is played before the screening of every cinema show in Thailand, when the audience stands to honor the king as pictures of his life and work are shown on the screen.
Saturday's singing was recorded for use in cinemas, organizers said.
"Since he went to heaven we want all Thais to demonstrate their love and sing this song to show before film screenings," Prince Chatri Chalerm Yukol, a movie director in charge of the filming of the singing, told reporters.
Since the king died, people from across Thailand have flocked to the gilded Grand Palace to pay homage to the only king most of them have ever known, who is lying in state there.
Buddhist monks have been chanting prayers beside his coffin in an imposing throne hall, and they will chant for 100 days as part of the funeral rites.
"I wanted to be here to pay respects to His Majesty," said Haysri Watanakulpipat, 47, who said she drove overnight from the eastern province of Prachinburi.
The military government has not set a date for the royal cremation but it is expected in about a year.
The government has said Crown Prince Maha Vajiralongkorn will ascend the thrown soon but he had requested that his succession be delayed for an unspecified period, so he can grieve with the people.
The government has moved to quash uncertainty surrounding the succession and to reassure the country that the king's death will not derail plans for a return to democratic rule, which include a general election in late 2017.
It has stressed business and government should carry on as normal and tourism should not be affected.
Police said they expected more people at Sanam Luang through the day.
"There are more than 150,000 people here already but it could easily rise to 250,000 by the evening," Thai deputy police spokesman Major General Songpol Wattanachai told Reuters.
The Grand Palace is a former royal residence that is used only on ceremonial occasions.
The royal anthem was the national anthem of what was then Siam until 1932, when young army officers and bureaucrats staged a coup to end absolute monarchy.
(Reporting by Amy Sawitta Lefevre, Aukkarapon Niyomat and Cod Satrusayang; Writing by Amy Sawitta Lefevre; Editing by Robert Birsel)