Vilasrao Deshmukh, Chief Minister of Maharashtra state of which Bombay is capital, told reporters that 147 people died in the blasts that took place inside compartments of local trains and platforms near stations in the western express suburb of the city. Bombay is also called Mumbai.
The bombs went off during the rush hour between 6.00 and 6.30 pm (7:30 and 8 p.m. Thailand time) near the Khar, Mahim, Jogeshwari, Borivali, Bhayander, Matunga and Mira Road suburban stations, officials said.
Police said more fatalities were averted as an eighth bomb on the rail network was defused.
No terrorist group has claimed responsibility for the blasts.
The local administration suggested that death toll was likely to mount, as a number of the 439 wounded had sustained serious injuries.
"Our immediate concern is to remove the injured to the hospitals. We hope the worst is over for Bombay," the state's top official D Shankaran said.
Many deaths occurred as blasts ripped through train compartments, hurling out mangled bodies of passengers.
Eyewitnesses said several others died as they tried to jump out of the trains that had caught fire.
Train carriages were completely wrecked with shattered window- panes and twisted steel fittings lay strewn around.
The blast inside the first-class compartment of a train at the Matunga railway station was so powerful that it tore through the train as well as a portion of the platform shed.
Scenes of commotion were witnessed at the railway stations as injured passengers, with blood on their faces, cried for help near the trains.
Other injured survivors limped out of the rail-tracks and tried to contact their family members on cellular phones.
Sudden rains rendered the rescue and relief operations more difficult as train commuters and residents of nearby areas pitched in for rescue efforts.
"It was a miserable scene, stomachs were torn open and limbs were lying around. Blood was splattered in the compartments as the coaches suffered extensive damage," said Dhiraj Kelkar, a commuter who was involved in rescue operations.
Many of the passengers in adjoining compartments, who were not wounded in the blasts, sustained injuries while trying to jump out of moving trains.
"The train was crowded when suddenly there was a loud explosion and the compartment was covered with fire and smoke. It was unnerving. I just managed to plunge out of the moving train," Anjali Sinha, a survivor said.
Panic and fear gripped the city as scores of train commuters were stranded and not able to travel due to suspension of train services.
The Bombay rail network is considered the life-line of the metropolis as millions commute on the network every day.
Over 6.1 million commuters travel on the network on a daily basis; the network has highest passenger density of any urban railway system in the world.
Police said terrorists were behind the blasts which were "coordinated" and "synchronized" to inflict maximum fatalities during the peak hour when people were on their way home from work.
"The way the serial blasts have taken place within 30 minutes, it is likely to be the work of terrorists," the city's police chief, AN Roy told the NDTV network.
The serial blasts were considered the worst terrorist attack in Bombay in over a decade.
In 1993, over 270 people were killed serial bombings in the metropolis allegedly carried out by the Bombay underworld and terrorists following the razing of the disputed Babri Mosque in the country's northern Uttar Pradesh state.
Suspected in the bombings are the Pakistan-based Lashkar-e-Toiba (Army of the Pure) militant group, which has been blamed for engineering several daring attacks in India.
In the national capital New Delhi, Indian Premier Manmohan Singh held an emergency meeting with Home Minister Shivraj Patil and senior officials to review the security situation in the country.
Emerging from the meeting Patil said Singh condemned the acts as cowardly and shameful and said that the country was resolved to "defeat the evil designs of terrorists."
"We reiterated that we will fight terror in all its forms and manifestations," Patil told reporters.
Delhi and other major Indian cities were placed on high alert soon after the attacks.