The strike has so far been peaceful but security forces are on high alert
The Maoist party in Nepal is enforcing what it says will be an indefinite strike, in an attempt to force the government to resign.
Thousands of Maoist opposition supporters, some armed with bamboo sticks, are out on the streets of the capital Kathmandu.
The BBC's Joanna Jolly says the country has come to a standstill, with businesses shut and roads empty.
Nepal's government is not supported by the people, the Maoists say.
Prime Minister Madhav Kumar Nepal has asked the Maoists to resolve their issues through dialogue.
"We have been accused of playing a conspiratorial role in the creation of the constitution by the main opposition party, when they should be helping and participating in a creative way," he was quoted as saying by Reuters news agency.
By Joanna Jolly in Kathmandu
The Maoists have said they will continue the national strike until the government resigns and they can take over the country.
So far the government is standing firm. Although talks are still continuing, there is no sign of a solution.
Meanwhile the country has come to a standstill. Businesses, factories, schools and offices have shut and there are no vehicles on the streets.
This has become a game of brinkmanship between the government and the Maoists with each side seeing if they can hold out longer than the other.
The Maoists say the government has not consolidated Nepal's peace process and has failed to draft a new constitution.
Most offices and shops have closed and only emergency vehicles are allowed onto the streets, the BBC's Joanna Jolly in Kathmandu says.
"The whole country is shut down. No institutions or industries are operating and there is no traffic," senior police official Bigyan Raj Sharma was quoted as saying by AFP.
The Maoists insist their protest will be peaceful, but police say they have already confiscated sticks, petrol bombs and explosives from supporters.
So far the atmosphere is festive, but the government has put the security forces on high alert and deployed extra police in the capital, our correspondent says.
The strike follows a mass May Day rally of tens of thousands on Saturday, when demonstrators demanded the resignation of Mr Nepal and his government.
"Revolution and major political changes in Nepal have come through street protests," AP quoted Maoist leader Pushpa Kamal Dahal as telling the crowd Saturday.
The Maoists, the largest party in parliament, want to lead a national unity government.
They briefly led a coalition government in 2008, but it split in 2009 following a dispute over the sacking of the army chief.