A Chinese restaurant, which had about 15 people inside, and a dance studio for children, which was unoccupied at the time of explosion, were among the buildings destroyed in the blast at Bebbington town.
Merseyside fire and rescue service said the explosion was a major incident.
"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. It's a very significant debris field and (there is) lots of structural damage to the surrounding buildings," said Dan Stephens, chief officer at Merseyside Fire and Rescue Service.
Chief Inspector David Westby of Merseyside Police said an investigation was under way to establish the exact reasons behind the explosion.
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He said: "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."
An eyewitness who lives close to the site said the explosion sounded like an "earthquake".
"Our whole house shook. It sounded like the windows were about to smash in," she said.
Wirral South MP Alison McGovern went to the scene and described it as a "very serious" situation.
Amessage posted on the Complete Works dance studio 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 600 pounds has already been donated to help the dance school recover from the loss of its building.