HAVERHILL, Mass. (WHDH) -- Police in Haverhill are stepping up security on school buses in the wake of two pellet gun shootings that blew out windows.

A police officer will be on each school bus Friday and extra patrol cars will be along each route after someone used a BB or pellet gun to blast out bust windows right about students’ heads.

The first attack happened at 11:30 a.m. Thursday on Main Street involving a bus carrying pre-schoolers. Pellets were fired again at bus, this time on Winter Street, filled with high school students at 2:30 p.m. Police said someone most likely took aim at the buses while in a moving car. The two incidents happened one mile apart.

“There were children sitting in seats where the window was shattered and they did have glass that did fall on top of them,” said Lt. Robert Pistone, Haverhill Police Department.

Following the deadly shootings at Sandy Hook Elementary School, Haverhill Police had already assigned extra patrols to the schools. Now, they're putting officers aboard the buses.

“Someone is pulling a prank or something that has caused a tremendous amount of anxiety on the part of the school people and parents and the community at large,” said James Scully, Superintendant of Haverhill Public Schools.

With stress over school safety running high, the two hits are only adding alarm.

“It’s supposed to be a magical time of year for students and families as they celebrate the holidays. This type of behavior on top of the tragedy raises everybody's anxiety,” said Scully.

No one was hurt in the two incidents.

The buses are equipped with surveillance cameras. Officers will review the footage from the cameras to see if they can gain any additional information about a suspect.