Media playback is unsupported on your device Media caption No-one has crossed the Pacific Ocean in a gas balloon since 1981, as Alistair Leithead reports

Two pilots have surpassed the world distance and duration records with a flight across the Pacific Ocean in a helium balloon.

American Troy Bradley and Russian Leonid Tiukhtyaev left Japan on Sunday and had aimed to land in Canada or the US.

However, weather has forced them to change course towards Mexico where they are due to land sometime on Saturday.

To set records the team needed to beat the existing records by 1%.

For duration that meant staying aloft for about 138 hours and 45 minutes to beat the existing record set in 1981.

For distance that meant a journey of about 5,260 miles (8,465km) to beat the existing record of 5,209 miles set in 1981.

The hi-tech "Two Eagles" balloon is made of a strong Kevlar and carbon-fibre composite, but weighs only 220 pounds (100kg).

It is fitted with monitors and other instruments that track their course and compile data to be submitted to record-keepers.

The specially-designed capsule sits beneath a huge helium-filled envelope and is designed to stay aloft for up to 10 days. The pilots live in a closet-like space with a very low ceiling.

Image copyright AP Image caption The Two Eagles balloon is capable of staying aloft for up to 10 days

Image copyright Troy Bradley/Two Eagles Image caption The gas balloon took off from Saga, Japan, on 24 January

Image copyright Troy Bradley/Two Eagles Image caption The colour-coded cords help the pilots know how much ballast or expendable weight is used during the flight

Image copyright Troy Bradley/Two Eagles Image caption The balloon is set to land in Mexico after weather conditions changed the flight plan

On Thursday, the Two Eagles team tweeted: "The pilots have just surpassed the distance needed to set a new record. 5,261 miles or 8,467km."

"We're not taking any time to celebrate,'' said head of mission control Steve Shope.

"We have a lot of work we have to do, and we're just taking this flight one hour at a time."

On its website, the team says Two Eagles will not have officially broken the records until documentation is approved by the US National Aeronautic Association followed by the Federation Aeronautique Internationale - a process that could take several weeks or months.

In 1978, three pilots made the first trans-Atlantic balloon flight in 137 hours, 5 minutes and 50 seconds, setting the duration record in the process.

Americans Ben Abruzzo, Maxie Anderson, and Larry Newman travelled on the Double Eagle II balloon from Presque Isle, Maine, to Miserey, France, about 60 miles (95km) northwest of Paris.

The Double Eagle II gondola is displayed at the Smithsonian National Air and Space Museum annex at Washington Dulles International Airport.

Two Eagles facts

The Two Eagles craft is a helium-filled gas balloon. "Roziere Balloons", which use both hot-air and gas, are the only ones that have circled the earth.

Depending on weather conditions, the balloon flies between 12,000 to 30,000 feet (9,100m) above the ground

The craft is about five feet (150cm) wide, seven feet long, and five feet high, weighing only 220 pounds (100kg).

The balloon started its journey carrying about 11,000 pounds of sand for ballast

In 1981, the Double Eagle V was the first gas balloon to successfully cross the Pacific Ocean and set the existing distance record.

Crew members Mr Abruzzo, Mr Newman, Ron Clark and Rocky Aoki made it from Nagashima, Japan, to Mendocino National Forest in California in 84 hours and 31 minutes.

The current team named its craft in honour of the existing record holders.

Two Eagles can stay in the air for a maximum of 10 days; it is now day five of the journey.

At the moment, it is not clear exactly where the Two Eagles balloon will land.

The team had been aiming for Canada but a ride of high-pressure ridge off the US West Coast forced the balloon into a sweeping right turn toward Mexico.

A network of balloon enthusiasts has been organised to act as chase crews, but correspondents say it remains unclear if the balloon will be able to land in a place where a ground crew can help them.