Mumbai, India's largest commercial city, opened its first fully underground metro line earlier this month with help from Japan. It is expected to ease traffic congestion and boost business opportunities.

The Mumbai Metro Line 3 will be more than 33-kilometers-long, out of which about 13 kilometers opened this month. The line connects the city's international airport to commercial districts and even a world heritage site. This is Mumbai's first line that runs entirely underground. The total project cost is more than 4.5 billion dollars, of which Japan is providing more than 2.3 billion dollars in yen loans.

The metro system is projected to transport 1.5 million passengers daily.

In the inauguration ceremony, Prime Minister Narendra Modi said: "The people of Mumbai have been waiting for the metro line for a long time. I would like to express my gratitude to the Japanese government."

The Metro Line 3 is expected to be fully operational in March next year.