Ferry's cleaners discovered the weapons Saturday morning, October 28, soon after the boat arrived in UK waters.
Officers were alerted, but it is still not clear how the weapons had passed through security checks. However, they are not believed to be part of terrorist plot.
According to Kent Police spokesman the guns had been safely removed by police and investigation had been launched.
The operator, P&O Ferries, announced it was working with authorities to ensure passengers were safe.