Afghanistan declared the start of Ramadan on Tuesday after religious scholars sighted the moon, along with Muslims in the Philippines.
Indonesia, the world's most populous Muslim nation, started the month of fasting on Wednesday along with Malaysia and Thailand while Bangladesh and India are likely to follow suit.
Pakistan is set to usher in Ramadan on Thursday.
In Afghanistan, which is slowly clawing its way back from two decades of war, people are still suffering without any basic amenities.
"It's full-time Ramadan here," said Kabul businessman Bahram Sarwary, 33. "In Afghanistan most of the people don't have food to eat, there is no drinking water."
Shopkeeper and former lawyer Ruh Allah Stankzai said the month of fasting was a time to appreciate the progress the country had made since last year.
"This year it's good because we've the parliament," he said, referring to parliamentary elections on 18 September.
Prayer calls early on Tuesday in the Philippines ushered in Ramadan for millions of Muslims in the south of the country.
"It's full-time Ramadan here. In Afghanistan most of the people don't have food to eat, there is no drinking water"
The separatist Moro Islamic Liberation Front (MILF) said it would help secure the peace in the Philippines during Ramadan.
In Thailand, the government said state-owned television would broadcast to villages in the country's south nightly prayers from Saudi Arabia in which the Muslim holy book is recited.
"We are being careful" during Ramadan, Thai Defence Minister Thammarak Issarangkura Na Ayutthayahe said this week.
Indonesia was starting Ramadan on Wednesday on a down note after the Bali bombings.
The start of Ramadan was preceded by an average 126% rise in fuel prices and a resulting increase in other commodities, goods and services.
"Unlike the Ramadan last year, Muslims in Indonesia are entering the holy month not only with joy, but also sadness," the Pikiran Rakyat daily, the country's largest rural newspaper, said in its editorial on Tuesday.
Prices and security were also the main concerns in Pakistan.
Additional police have been deployed at all mosques and security has been tightened across Pakistan, while special committees have been set up to control the prices of food items during Ramadan, officials said.
Bangladesh was hit by three bombs at courthouses on Monday, the latest in a series of attacks.
Indonesians saw an average
126% rise in fuel prices
But restaurants were getting ready for a busy month preparing the fast-breaking meal known as Iftar.
"Iftar provides fraternity and equality," said housewife Mousimu Khanom, 35, eating at the popular food stalls in the old quarter of the capital Dhaka.
There were also hopes for peace in Indian-administered Kashmir, where steadily improving relations between New Delhi and Islamabad have led to a lull in fighting.
Mufti Bashiruddin, the grand mufti of Kashmir, urged his people and the Indian security forces to call a ceasefire.
"Such a move, I'm confident, will have tremendous positive impact on the local population," he said.