President Barack Obama on Thursday eulogized 12 firefighters who were among 14 people killed in a massive blast at a fertilizer plant in a small Texas town, during a week of tragedy in America.

Obama told mourners of those killed in the town of close-knit town of West that they were not forgotten in the wake of last week's explosion, despite massive media attention focusing on the deadly bombings in Boston.

"To the families and neighbors grappling with unbearable loss, we are here to say, you are not alone. You are not forgotten," Obama said, with 12 caskets of draped in US flags in front of him, at a memorial service at Baylor University in the city of Waco.

"America needs towns like West -- that's what makes this country great," said Obama, lauding a place where everybody knew everybody else, and where many dead firefighters were volunteers.

"You have been tested, West. You have been tried. You have gone through fire. But you are and always will be surrounded by an abundance of love," Obama said.

The president, in the latest of a number of recent appearances at memorial services following a spate of recent tragedies, traveled to Waco from Dallas, where he attended the opening of George W. Bush's presidential library.

He said he brought good wishes from all the living US presidents who attended the event, and also highlighted the region's unique heritage as a destination for Czech immigrants.

The explosion in the town of 2,800 people killed at least 14 people and injured around 200 others.

Homes near the blast site were flattened, a 50-unit apartment complex was blown to bits and a nursing home and several schools were also badly damaged as fire spread from building to building.