Hundreds of thousands of Bangladeshi protesters demanding Prime Minister Sheikh Hasina resign clashed with government supporters on Sunday, with scores killed in one of the deadliest days since demonstrations began.

Rallies that began last month against civil service job quotas have escalated into some of the worst unrest of Hasina's 15-year rule and shifted into wider calls for the 76-year-old to step down.

At least 77 people were killed on Sunday alone, including 14 police officers, with the rival sides battling with sticks and knives and security forces firing rifles, taking the total killed since protests began in July to at least 283.

Police said protesters attacked their officers, including storming a station in the northeastern town of Enayetpur.

"The terrorists attacked the police station and killed 11 policemen," said Bijoy Basak, a deputy inspector general.

Witnesses in Dhaka reported hearing sustained crackles of gunfire after dark on Sunday, with protesters defying a nationwide curfew.

At least 12 people were killed in the capital, police and doctors at hospitals said, several with bullet wounds, while 18 were killed in Bangladesh's northern district of Sirajganj.

Mobile internet was tightly restricted countrywide.

In several cases, soldiers and police did not intervene to stem the protests, unlike the past month of rallies that repeatedly ended in deadly crackdowns. (AFP)