Three inmates, including an accused murderer, who broke out of a maximum-security prison by climbing down bedsheets are still on the run, three days after escaping.

A massive manhunt has been launched for Hossein Nayeri, 37, Jonathan Tieu, 20, and Bac Duong, 43, who escaped from a jail in Orange County, California.

The trio, who were last seen on Friday evening, cut through a steel grate inside their cell, climbed through a plumbing tunnel and up to the roof of the facility. They then used bedsheets to lower themselves down four stories before disappearing, authorities said.

"We're exhausting every lead that we currently have," Orange County sheriff's Lt. Jeff Hallock said.

He said authorities are investigating whether the trio had help from inside or outside the prison.

Tieu has been held at the facility since October 2013 charged with murder.

Duong was being held on charges of attempted murder and other counts, while Nayeri is accused of kidnapp and torture.

A $50,000 (£35,000) reward has been offered as police hunt for new leads in the case.

Nayeri, an Iranian, is one of four people accused of kidnapping and torturing a marijuana dispensary owner, the Register said. He has been held in the jail without bail since September 2014 after being arrested by the FBI in Prague.