Eighteen-time Olympic gold medalist Michael Phelps has apologised after being arrested for drink-driving.

Olympic swimming superstar Michael Phelps had bloodshot eyes and slurred speech when he was pulled over and arrested for drink driving, according to police documents.

Phelps was arrested on Tuesday in his home state of Maryland. A breathalyser test showed a blood-alcohol level of .14, well above Maryland’s legal limit of .08.

Phelps, the most decorated Olympian of all time with 22 medals including 18 gold, says he is deeply sorry for his actions.

The 29-year-old was pulled over after his white Land Rover was clocked at 135 km/h in a 72 kp/h zone in a Baltimore road tunnel.

The arresting officer described “a strong odour of an alcoholic beverage emitting from the vehicle”, according to documents obtained by the Baltimore Sun.

“I observed that the operator’s eyes were red, bloodshot, and his speech was mush mouth,” the officer said.

Phelps had “trouble maintaining his balance” when performing a walk-and-turn sobriety test, and declined a test of balancing on one leg.

Phelps, who was been charged with driving under the influence, excessive speed and crossing double lines, told the officer he had consumed “three or four” drinks at the newly opened Horseshoe Casino.

Phelps expressed his remorse on social media.

“I understand the severity of my actions and take full responsibility,” he told his 1.6 million Twitter followers.

“I know these words may not mean much right now but I am deeply sorry to everyone I have let down.”

It’s not the first time Phelps has found himself in such circumstances.

Ten years ago he pleaded guilty to driving while impaired in rural Maryland. He was sentenced to 18 months’ probation and fined $250 for what he later described as an “isolated incident.”

He was under the microscope again in 2009 when a photograph of him apparently smoking a marijuana pipe was published in a British tabloid and went viral.

He was suspended from swimming for three months.

Phelps retired from competitive swimming after the 2012 Olympics in London, but launched a comeback earlier this year.

He made a dazzling return to international competition last month, winning three gold medals at the Pan Pacific Championships on Queensland’s Gold Coast.

His strong showing bolstered hopes that he might compete at the 2016 Olympics in Rio de Janeiro.