A subway tunnel under construction collapsed in Beijing last week and buried six migrant workers. The collapse is the third major accident on that particular subway line in just over a year, the Wall Street Journal reported. Authorities said over the weekend that four people died. State media said an attempt was made to cover up the incident, highlighting the pressure on more than 10,000 construction sites across the capital. Police have arrested 10 people in connection to last week's collapse but the labor contractor appears to have fled, the newspaper reported. The line is part of a US$40 billion construction boom ahead of the Olympics next year. The push to have everything ready on time has led to round-the-clock work for armies of migrant workers with some shifts lasting as long as 24 hours.