Hundreds of activists poured in on Dhaka roads as Zia headed to court.
Bangladesh opposition leader Khaleda Zia was convicted of corruption and sentenced her to five years in jail on Thursday as police clashed with thousands of her supporters outside the court.
Khaleda's son, Tarique Rahman, and four others - a lawmaker, Zia's secretary, her nephew and a businessman - were jailed for 10 years each at the end of a case that lasted almost 10 years.
After the verdict, she was taken at the Woman Cell and Daycare Centre at the old Dhaka Central jail.
Bangladesh security forces have previously used excessive and indiscriminate force to contain political protests.
Zia, 72, was sentenced by the Special Court-5 in the capital, Dhaka, in connection with misappropriation of 21 million takas ($252,000) in foreign donations meant for the Zia Orphanage Trust.
The conviction means Zia, the longtime rival to the current prime minister, could be barred from running in December national elections.
BNP's joint Secretary General Ruhul Kabir Rizvi said the sentence was a "blueprint to destroy Begum Khaleda Zia,"adding that the "people of Bangladesh will reject this verdict". He added that many people would see it as a tactic for removing the main contender in the election and a way of "demonising a political opponent".
The BNP can not afford to stay away from the polls this time.
The BNP had boycotted the last election held in 2014, demanding that the elections be held under a caretaker government. But later in the evening, some incidents of violence were reported.
Zia's lawyer, Khandkar Mahbub Hossain, said the ruling was "political vengeance" and would be overturned by a higher court. According to the analyst, bail is a certainty.
The judge read out the abridged version of the 632-page verdict in 10 minutes while several BNP leaders were present in the courtroom.
Judge Mohammad Akhteruzzaman said he was satisfied that the court had proved the charges against Zia, and said the sentence had been made more lenient than it would have been otherwise.
The BNP will face double trouble as Khaleda's son, the London-based Tarique, has been in absentia for over a decade. Concerns have also been raised that Awami League and BNP supporters might provoke violence and target each other's supporters, Human Rights Watch said. Thousands of supporters took to the streets of the capital to protest the ruling. Anticipating blockades and protests, the government had detained several senior BNP leaders, while several others have gone into hiding. "We encourage the government of Bangladesh to ensure fair trial guarantees for all of its individuals in Bangladesh", the spokesperson said.