Donald Trump's "big, beautiful wall" at the Mexican border should be 30-foot high, look good from the American side and be difficult to climb or cut through, according to a contract posted on a government website.

The contract notices were made public by Customs and Border Protection (CBP), the Homeland Security Department agency which will oversee the project and eventually patrol and maintain the wall.

The proposed wall must be built in a such a way it would take at least an hour to cut through it with a "sledgehammer, car jack, pick axe, chisel, battery operated impact tools, battery operated cutting tools, Oxy/acetylene torch or other similar hand-held tools."

The north side of the wall, which will face the US, "shall be aesthetically pleasing in colour, anti-climb texture, etc., to be consistent with general surrounding environment." No specifications were given for the side facing Mexico.

Trump doesn't say who will pay for Mexico wall, only that it's coming

One of the contract requests calls for a solid concrete wall, while the other asks for proposals for a see-through structure. Both require the wall to be sunk at least six feet into the ground to deter anyone from tunnelling underneath it.

The government will award a contract based on 30ft wide sample walls to be built in San Diego.

Last month CBP put out a call for "concept papers" to design and build prototypes by 10 March.

Mr Trump has bragged in recent days the wall is ahead of schedule.

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The government has not said where the wall will be built, though the contract notices suggest some pieces of a new wall could replace existing fencing that stretches over about 700 miles of the roughly 2,000-mile border.

The current fencing of mixed construction, including 15ft steel posts set inches apart designed to keep people from crossing and shorter posts that are intended to block cars. Border Patrol agents are constantly repairing holes in the structure.

Mr Trump has long promised Mexico would pay for the wall, which he has said is necessary to stop the flow of immigrants crossing the border illegally and drug smugglers.

This week the President sent a budget proposal to Congress including a $2.6bn (£2bn) down payment for the wall.

The total cost is unclear, but the Government Accountability Office estimates it would cost about $6.5m (£5m) a mile for fence to keep pedestrians from crossing the border and about $1.8m (£1.5m) a mile for a vehicle barrier.

Congressional Republicans have said Mr Trump's wall would cost between $12bn (£9.7bn) and $15bn (£12bn). Mr Trump's suggested cost is closer to the lower estimate.