* Police break up election clashes in West Bengal state
* Financial capital Mumbai included in latest round of voting
* More than 127 mn go to polls in fourth phase of election
* PM Modi fights election on tough security stand
* Last round of voting May 19, results four days later
Police broke up clashes between rival groups of voters in a key eastern state on Monday as some of India's richest families and Bollywood stars also cast their ballots in Mumbai during the fourth phase of a massive, staggered general election.
In West Bengal, a populous eastern state crucial for Prime Minister Narendra Modi's re-election bid, supporters of his Hindu nationalist Bharatiya Janata Party (BJP) clashed with others from the regional Trinamool Congress, police said.
TV footage showed armed security forces chasing away people wielding sticks, although it was initially difficult to determine the scale of the clashes.
There were no immediate reports of any poll-related injuries in West Bengal, where at least one person was killed and three injured during the third phase of voting last week.
The BJP is in a direct, and sometimes bloody, fight in West Bengal with Trinamool, whose chief Mamata Banerjee is one of Modi's biggest critics and a potential prime ministerial candidate.
More than 127 million people are eligible to vote in this round of the seven-phase election held across 71 seats in nine states. Modi's coalition won more than 75 percent of the seats in the previous election in 2014.
Many of the constituencies are in Uttar Pradesh state in the north and western India's Maharashtra, where the financial capital Mumbai is located. Uttar Pradesh elects the most lawmakers, with Maharashtra next. Both states are ruled by the BJP and its allies.
However, political analysts say the BJP may struggle to repeat its strong showing this time due mainly to a jobs shortage and weak farm prices, issues upon which the main opposition Congress party has seized.
First-time voter Ankita Bhavke, a college student in Mumbai, said she voted for economic development.
‘I want the country to be at par with the best in the world,’ she said. ‘There's been some progress in the last five years.’
India's financial markets were closed on Monday for the election.
Mumbai is home to the massive Hindi film industry, as well as Asia's wealthiest man, Mukesh Ambani, and India's richest banker, Uday Kotak.
Ambani, who heads Reliance Industries, and Kotak, managing director of Kotak Mahindra Bank, created a stir this month by publicly endorsing an opposition Congress party candidate from their upscale South Mumbai constituency.
Mumbai, which has six seats, is India's wealthiest city but ageing and insufficient infrastructure is a major concern. Six people were killed last month when part of a pedestrian bridge collapsed, recalling memories of a 2017 rush-hour stampede that killed at least 22 people on a narrow pedestrian bridge.
The election, the world's biggest democratic exercise with about 900 million voters, started on April 11 with Modi in the lead amid heightened tension with long-time enemy Pakistan.
The last phase of voting is on May 19, with results released four days later.
There are a total of 545 seats in parliament's lower house.
Modi sent warplanes into Pakistan in late February in response to a suicide attack by a militant group based there that killed 40 Indian police in the disputed Kashmir region.
Modi has sought votes on his tough response towards militancy and in recent days has evoked the deadly Easter Sunday bombings in nearby Sri Lanka.
Maidul Islam, a professor of political science at Kolkata's Centre for Studies in Social Sciences, said long queues outside polling stations would indicate whether Modi's national security pitch was working.
‘Whenever there is a BJP kind of a wave, you see a higher voter turnout,’ he said.