Clashes between rival activists in the northern town of Natore involving guns and several small bombs left 20 people with bullet wounds.
"More than 20 people, including the local party chief of the Bangladesh Nationalist Party (BNP), were hurt by bullets during clashes with the opposition Awami League," said police officer Liakat Ali.
"Supporters of both parties clashed with guns and bombs at the heart of the town as both wanted to hold rallies there," said Ali, adding that police used tear gas to disperse the crowd.
Thousands of rival party supporters took to the streets of the otherwise deserted capital Dhaka to stage rallies and demonstrations.
Roads and train tracks linking the country's main cities were blocked by opposition supporters, police and officials said.
"The capital has been cut off from the rest of the country," said Aurangjeb Mahbub, the deputy commissioner of Dhaka Police.
Cars were off the streets in main cities, while schools, offices and businesses were closed.
Deliveries to and from the country's main port in south-eastern Chittagong came to a standstill, said port director Kamrul Hasan.
"Over 14,000 police and paramilitaries have been deployed in the capital to avert any violence," said police inspector Mahbubur Rahman.
Business leaders have appealed for an end to the protests, saying they are costing the impoverished country's textile industry at least 70 million dollars a day.
Private television channels showed a number of incidents in which one police officer was injured and several vehicles were destroyed by opposition activists.
The main opposition Awami League called the protest action after last-ditch talks with President Iajuddin Ahmed broke down over his failure to replace chief election commissioner M.A. Aziz.
A caretaker government delegation also met Aziz on Monday but officials refused to be drawn on the discussions.
The Awami League and its allies on Wednesday had called off a four-day blockade, saying they would give the president and head of the caretaker government, in place to oversee free and fair polls, until Sunday evening to meet their demands.
The opposition alliance accuses Aziz, a former Supreme Court judge, of stacking the cards in favour of the outgoing BNP-led government by drawing up a voter list with 10 million fake voters.
Interim cabinet member Mahbubul Alam has said that the government has come up with a package of measures it believes will end the impasse.
The president was expected to reveal the proposals in a televised address to the country in the next few days.
One of the measures already made public has been the appointment of two new election commissioners, but the opposition says this will only be acceptable if they replace Aziz and one of his deputies.
The blockade is the latest in a string of protests staged by the Awami League against BNP-appointed officials it considers politically biased.
Some 25 people died in four days of clashes between rival parties from October 27, when the BNP's five-year mandate expired.
BNP leader Khaleda Zia led a four-party, coalition government until handing over to the interim body. Her party has threatened to hold more protests if Aziz is removed.

Copyright AFP (Agence France-Presse), 2006