LAWRENCE, Mass. (AP) - The company that owns Columbia Gas says its crews are performing safety checks after a series of fires and explosions erupted in three communities north of Boston, but did not explain what went wrong.

A statement from Indiana-based NiSource says its "thoughts are with everyone affected by today's incident" and that it appreciates the response from local emergency crews.

State and local officials said at a news conference minutes earlier that they had still not heard from Columbia Gas following the fires in Lawrence, Andover and North Andover. Gov. Charlie Baker later clarified that he thought the company's response was "adequate."

Authorities are blaming over-pressurized gas lines and previously told all residents with Columbia Gas service in those areas to evacuate.

At least six people were injured in the fires and explosions, including two in critical condition.