GARISSA, Kenya - Unknown armed gunmen suspected to be Al-Shabaab militants on Thursday morning attacked a university college in Garissa near the border with Somalia and held student hostages.

Police and witnesses said the masked gunmen stormed Moi University's College in the town at around 5:00 am, and started their killing from mosque within the facility.

Gunshots and explosions were heard from the compound for hours as police and military were mobilised there.

Kenyan authorities have not confirmed the number of casualties.

According to witnesses, the gunmen went into the university as most of them went for morning prayers, and those calling from inside the university said there were many casualties.

Kenyan government troops have surrounded the compound, and ambulance sirens rant the air amid massive casualties.

Unconfirmed reports that six heavily armed suicide-vested fighters were inside the college as gunfire was still ongoing.