The entrance to Buncefield Oil Depot in Hemel Hempstead has been blocked by Just Stop Oil protesters.
Officers from Hertfordshire Police are at the scene, and are attempting to diffuse the situation.
Meanwhile, roads around the depot have been closed off, and the general public are being kept away from the area.
An individual at the location told the Herts Advertiser that the protesters had blocked the entrance to the part of the depot where fuel is kept, halting workers' ability to access the resource.
It started snowing on the protesters at around 12:20, shortly after an ambulance had arrived, at around 11:50pm.
Similar protests are also taking place in ten other oil depots across the country, and ExxonMobil UK have temporarily stopped operations at four terminals.
Along with Extinction Rebellion members, Just Stop Oil claim that 500 supporters of the movement remain at ten oil terminals, with potential disruption to fuel supplies in London and the South East.
A spokesperson from Hertfordshire Police said: "We are currently dealing with an incident in Green Lane, Hemel Hempstead, where a number of people are blocking the entrance to a site.
"Our officers are currently working to resolve the situation safely, and nearby roads may be affected as a part of this.
"We are urging people to avoid the area where possible and plan their journey accordingly.
"We appreciate your patience and understanding."
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