Bangladesh Prime Minister Sheikh Hasina on Monday visited suburban Savar to review the rescue work at following the collapse of an eight-storey building last week that killed nearly 400 people, even as rescuers lost hope to find more survivors after a fire broke out in the rubble.

Ms Hasina talked to the rescue officials about the progress of the salvage campaign and went to a nearby private facility and a military hospital where the critically wounded survivors were being treated.

Television footage showed army troops cordoning off half a kilometre area around the collapsed Rana Plaza site, restricting entry of grim-faced relatives and onlookers at the site where army engineers mobilised heavy machinery to remove tonnes of concrete and rubble.

The structure, that housed five garment factories, a bank branch and around 300 shops employing thousands of workers, collapsed on April 24. The official death toll so far is 397.

“We are now launching the second phase (of the rescue campaign),” commander of the salvage operation Major General Chowdhury Hassan Sarwardy told reporters soon after midnight. After four days of rescue, 2443 people have been rescued.

In the first phase, rescuers crawled inside the rubble using small concrete and rod cutters fearing use of heavy machines could shake the concrete ruins endangering further the survivors inside the ruins of illegally built Rana Plaza.

But they went for the mechanical methods after hours of frantic effort to rescue alive the last detected survivor was disrupted by a fire, sparked from a rod cutting saw, apparently killing the woman.

“It is very unlikely that someone is still alive under the rubble without sufficient air and water... But Allah knows better,” a senior fire official told reporters as asked if they still expect anyone to survive.

Meanwhile, the fugitive owner of the building Sohel Rana was arrested by the elite anti-crime Rapid Action Battalion from Benapole, one of the 14 land ports with India, just as he was about to cross into West Bengal, making his arrest the fifth in the case.

A senior fire brigade official earlier told reporters at the scene that the time limit for manual rescue operations were extended as several survivors were found “miraculously” alive even hours after expiry of 72 hours, a time frame considered maximum for survival under such debris.

The last few hours of the first phase also yielded frustrations for rescuers as one of them with a choked voice described how a young girl appealed to him saying “don’t leave me brother” before taking her last breath.

Another woman volunteer cried out in extreme frustration, saying she could not save a young boy namely who “embraced me inside the debris saying please, please save my life.”

The authorities earlier on Monday said they were set to launch the second phase of the salvage campaigns as they found little rhythm or pulses of life under concrete rubble or in between sandwiched floors of Rana Plaza.

Rescuers initially set up equipment apparently selecting the midpoint of the collapsed structure as Sarwardy earlier said they would enter into the rubble on crane boxes creating boreholes from the top and pull out the survivors, if found.

Officials rescuers were now selecting calculated sites for creating boreholes to enter inside so the survivors or bodies could be retrieved safely.