HELSINKI, Finland (CNN) -- At least one person has been killed in a school shooting in Finland, CNN has learned.

The headmaster of the school in Tuusula, near Helsinki, is reported to have died in the attack, according to a reporter for CNN affiliate station MTV.

Some media reports have put the number of dead as being at least three. Police are telling reporters on the ground that at least one person is dead with several others injured

Jarkko Sipila, a reporter with MTV, told CNN that the shooting happened around noon Finnish time (10:00 GMT) in the quiet town around 50 kilometers (30 miles) north of Helsinki.

He said that at least four people had suffered gunshot wounds and that others had been injured by shattered glass.

Sipila said the gunman is believed to be an 18-year-old student and to currently be holed up inside the school, the channel said.

Local media say that police have surrounded and sealed off the school. Some pupils are said to still be in the school, although it is unclear whether the gunman has any hostages.

The Associated Press reported Heidi Hagman, assistant to the municipality director for Tuusula as saying that: "Some of the pupils have managed to escape from the school, but others are still inside."

The school is believed, according to local media, to be Jokela High School, attended by more than 400 students, aged between 12 and 18