At least two million Muslims attended prayers near the Bangladeshi capital as the second largest annual Islamic festival after the hajj began on Friday, officials said.
This year's World Muslim Congregation or Bishwa Ijtema in Tongi district is being held in two phases to accommodate an ever growing number of devotees, the district's chief government administrator, Kamal Uddin Chowdhury, told AFP.
"There are at least two million Muslims here on Friday, and hundreds more are joining the gathering every moment," Mr Chowdhury said.
In 2010, at least four million Muslims attended the festival.
The gathering, at which Muslims pray and listen to religious scholars, was first held in the 1960s on the banks of the Turag river.
It was launched by Tablig Jamaat, a non-political group that urges people to follow the tenets of Islam in their daily lives.
"The 165-acre (66.7 hectare) congregation ground has already been filled. People are now gathering in every open space," Mr Chowdhury said, adding the number of pilgrims is expected to grow until the concluding prayers on Sunday.
"Up to 25,000 foreigners from over 100 countries are attending the conference," Mr Chowdhury said, adding Prime Minister Sheikh Hasina was expected to join the prayers on Sunday.
The government has arranged special trains and ferries to transport pilgrims to the event, while army engineers have set up dozens of makeshift bridges and water tanks to accommodate the huge crowd.
Bangladesh is the world's third-largest Muslim-majority nation, with Muslims making up nearly 90 per cent of its 144 million population