Ajirin bin Ajiban, 26, a Filipino, is still at large, while Malaysian Azman bin Mamat, 35, was promptly arrested within 100 meters from the lock-up.
Labuan Police Chief Supt Adzhar Othman described Ajirin as dangerous.
The pair took advantage of permission by personnel on sentry duty to wash up before having their dawn meal in preparation for fasting.
Lance Corporal Ravindran Narayan had the cell keys when Azman punched him from the front, while Ajirin hit him on his head with a hard object before they snatched the cell keys from him.
His fellow sentry came to his assistance and gave chase.
Ravindran suffered minor head injury and was given outpatient treatment at the Labuan Hospital. Ajirin was caught for alleged armed robbery with an accomplice on May 23 under Section 395/397 which carries up to 20 years' jail and mandatory whipping.
He was remanded without bail as he had no legal papers and was waiting for his case to be heard on July 17. At the time of the escape, it was raining heavily and Ajirin was only in his underwear after he stripped off his red lock-up pants.
"Being a drug addict, he would not be able to stand the chill air for long," said Adzhar.
Azman was remanded since April 14 when he was arrested for alleged theft. Charged under Section 308 on April 23, he pleaded not guilty and was awaiting trial on July 17.
Armed police mounted roadblocks all over the island, especially the road leading to Kiansam and Kg Muslim, which are the Filipino enclaves and all exit points, including ungazetted jetties.
The marine police, maritime enforcement agency and the Marine Department are lending support to the operation.
Police in Menumbok, Beaufort and Sipitang had also been alerted of the manhunt.
Adzhar warned that sheltering an escapee is a serious offence and offenders could be jailed seven years and fined.
He appealed to the public for tip-off and information leading to the arrest of the detainee.
According to Adzhar, the two police on sentry duty would be investigated for negligence leading to the breakout.
The closed circuit camera television would provide the evidence of how the escape took place, he said.