Emergency services were called to a "major incident" in Bebington, Wirral, at about 21:15 GMT.
The buildings destroyed included a dance studio for children in Boundary Road, which was unoccupied at the time.
The injured were taken to hospitals in Merseyside and Chester, North West Ambulance Service (NWAS) said.
A number of houses in the immediate area were evacuated and more than 100 people moved to a nearby church, NWAS added.
Dan Stephens, chief officer at Merseyside Fire and Rescue Service, said the scale of damage is considerable.
"It's what we would describe as a total collapse, or the explosion has blown the walls out, which has caused the roof to collapse," he said.
"It's a very significant debris field and [there is] lots of structural damage to the surrounding buildings."
The seriously injured people were taken to Aintree Hospital in Liverpool. Others, less badly hurt, were treated at the Countess of Chester and Arrowe Park hospitals in Merseyside. One person was taken to the Royal Liverpool Hospital, NWAS said.
A police investigation is under way.
"We've got officers at all the hospitals. Detectives are gathering the relevant information in relation to victims and we will commence the investigation... from this point on," Ch Insp David Westby of Merseyside Police said.
The fire service has warned that the after effects of the explosion will last for some time.
"This incident is likely to be protracted. This is likely to last several days. There is very significant damage, so it will be some time before people will be allowed back into their homes," Mr Stephens said.
The violent explosion was heard by many people living in the Bebington area, Lew Hopkins, who lives close to the site, said: ""It sounded like an earthquake. Our whole house shook. It sounded like the windows were about to smash in.
"I know people about five, six miles away and they heard the explosion as well. Straight away I ran into the street and all the neighbours were outside."
Another resident, Mark Hamley, said: "There was a sense of quiet at first. Then you'd hear the odd shout or scream and cry.
"My main concern was for my girlfriend and my baby. I wanted to know they were safe. I put some clothes on, went outside and by the time that happened, the police were on the scene."
Josh Parry of The Liverpool Echo told BBC News the dance studio was next door to a Chinese restaurant, where a number of customers may have been injured.
He described a "significant" emergency response with about 12 ambulances and between 30 and 40 firefighters on site.
"There's been a huge amount of National Grid workers here, a huge response from the fire and ambulance and police, but also five or six accounts from people in the area that said yesterday they could smell gas in the area.
"That has not, I must stress, come officially from anywhere yet, but that is something that a number of people who live in the area have said to me," he added.
Local MP Alison McGovern said: "I live in New Ferry. I obviously felt it, didn't know what it was and then it became clear that there had been this very large explosion.
"There's very, very little we can say at this point. I would just ask people to stay away if they can, keep clear of the area and just let the police and the emergency services do their job."
A local churchman, pastor Aaron Partington, opened the doors of the My Life Church in Bebington to offer food and shelter to residents forced from their homes.
"There's been over a hundred people through the doors here. There's been a lot of stunned people," he said.
"A lot of people just feeling really, really at a loss.
"You kind of see this stuff happening on the news in other places, you don't really think it's going to happen on your doorstep."
A message posted on the Complete Works Facebook page said: "We are absolutely devastated that our lovely dance studios were impacted by tonight's events but first and foremost we are so very grateful that no one was in them at the time and now we hope there are no serious injuries and that everyone local is safe."
More than Â£600 has already been donated to help the dance school recover from the loss of its building.
Lauren Dickson, who set up the Just Giving page to raise funds, wrote: "Please donate anything you can to get Complete Works studios back on their feet.
"Complete Works was a home to 100s of children taught by hardworking Kim McDonald and Victoria Charlton. A devastating gas leak destroyed the whole building and all its contents."
Two people have been seriously injured and 32 others hurt following the collapse of several buildings after a suspected gas explosion on Merseyside.