It is less than two weeks since Western Australia's Premier Mark McGowan said he had no plans to close the state's eastern border.

Key points: Intrastate border closures have divided WA into nine separate regions

Intrastate border closures have divided WA into nine separate regions Police are patrolling regional highways to curb unnecessary travel

Police are patrolling regional highways to curb unnecessary travel Moving to another region without good reason could draw a $50,000 fine

Since then he has told out-of-state residents he does not "want [them] here", flagged a hard border closure could be in place by the weekend and implemented the toughest local travel restrictions in the nation.

The extraordinary measures, aimed to curb the importation and spread of COVID-19, include intrastate border closures, brought in today, that effectively divide the state into nine separate territories.

The new intrastate boundaries align with the areas covered by eight regional development commissions, excluding the Peel region which will be included in the Perth zone. ( Supplied: Department of Planning, Lands and Heritage )

People who cross into another region, without good reason, could face fines of up to $50,000.

WA Police said in the first 12 hours of the travel ban, about 6,000 people had been stopped at checkpoints throughout the state.

"We can tell you that 99 per cent of those people are doing the absolute right thing," Deputy Commissioner Gary Dreibergs said.

However, a tourist bus with 10 people on board was one of a number of vehicles turned around.

"We didn't prosecute, but I can tell you we will be prosecuting in the future."

While Tasmania has barred non-essential intrastate travel to Flinders Island, and the Northern Territory has limited access to its remote Indigenous communities to emergency personnel and health workers, WA is the first member of the Commonwealth to clamp down on interregional travel for its entire 2.5 million residents.

At a time he would usually be gearing up for an influx of Easter visitors, Great Southern Police Superintendent Ian Clarke said he had pivoted his officers from dealing with holiday crowds to patrolling the region's boundaries.

"Part of their role is stopping and talking to motorists about where they're travelling," he said.

"We have some permanent vehicle checkpoints that are in the outer metropolitan area but there's also highly mobile patrols that will do random vehicle check points as well as just general patrolling and stopping vehicles.

"Police are looking to support people as much as we can, but we do have a very clear mandate and that is to minimise the amount of travel that is occurring around the state so that we can do everything we can to minimise the spread of this virus."

Freight trucks and people travelling for work, including farmers and agricultural workers, are exempt from rules to limit traffic movement across the state. ( Mark Bennett )

Who is impacted?

The State Government has issued guidelines clarifying when it is OK to leave your region.

Here are the reasons that are permitted for interregional travel:

Travelling to work

Travelling to work Attending medical appointments

Attending medical appointments Transporting freight

Transporting freight Those who do not have access to groceries or supplies within their region

Those who do not have access to groceries or supplies within their region Returning to a place of residence

Returning to a place of residence Attending school or an educational institution

Attending school or an educational institution Where necessary, catering for family members

Where necessary, catering for family members Compassionate grounds

Superintendent Clarke said most people completing their daily work commute or local trip to the shops were unlikely to be stopped by police.

He said in addition to carrying driver's licences, police were recommending drivers carried some form of proof of employment if they were travelling to or from work, or proof of a medical appointment if they were travelling to see a doctor.

Police were out last night stopping motorists at a check point in Mt Barker on the major highway linking Perth and the state's south coast. ( ABC News: Mark Bennett )

Authorities were also working on an online form that could be used for people looking to apply for a formal exemption to travel between state boundaries.

"This will be another document that they will be able to carry with them as they [drive] through," Superintendent Clarke said.

"Police are very aware, as is government, about how much this has impacted on the broader community … I think people just need to remember that this is about crossing boundaries.

"If people are doing their normal day to day business travelling around their local areas this isn't going to impact them."

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He said police were taking a "compliance-with-compassion" approach to enforcing the travel bans, but the message to people unsure if they could travel was "if it's not essential, don't move".

Mr Dreibergs said police would soon set up a hotline to field "critical" questions about travel ban exemptions.

He said an app would also be developed within days to be used by the freight industry to streamline travel through checkpoints.

"The intent is that they will have an app that interacts with the police app and when they appear at a road checkpoint, they will just show that app to our police app and they'll continue to move through."