It follows an update to advice from the Public Health Services team, due to more cases of Covid-19 being recorded by the UK and European health authorities.
On Monday there were 4,368 daily cases in the UK, up 1,747 from the week before.
As part of the control measures to minimise the risk of transmission, inbound passengers will need to stay a distance of two metres apart.
Those passengers entering Guernsey by car should stay in the vehicle and follow any instructions by officials during the arrivals process.
'Passengers arriving and departing out of Guernsey Ports are strongly encouraged to follow Public Health Services guidance including the wearing of face masks where required, and to practice good personal hygiene measures that include regularly washing hands or using hand sanitiser,' a spokesperson said.
'Passengers transferring to Alderney should also observe these requirements while in the terminal and have any pick up arrangements confirmed in advance when they arrive into the island.'
For further Covid-19 information advice please visit: https://covid19.gov.gg/support/protect on the States of Guernsey’s website.
New rules were announced by the Government for England today that could last six months.
The new measures include 10pm closing for pubs and restaurants, a ban on indoor team sports and masks being mandatory for passengers in taxis.
People have been asked to again work from home if they can, barely a month after the UK government told everyone they should go back to the office.