KARACHI (AFP) River defences in flood-hit Sindh were bolstered Tuesday in a bid to save two towns from catastrophic flooding. Advancing floodwaters continue to threaten the towns of Johi and Dadu, with 19 of its 23 districts deluged and 2.8 million people displaced, according to provincial authorities. Armed forces and irrigation officials are racing against time to save Johi and Dadu, said provincial irrigation minister Jam Saifullah Dharejo. Floodwaters are increasing pressure on Johi embankment, while the raging waters are just five kilometres (three miles) away from Dadu city, Dharejo said. He said residents had formed a human chain to help reinforce embankments securing the towns. It is very heartening to us that local people are being very courageous and helping authorities, picking up stones to reinforce the embankments, he said. Dadu and Johi are about 320 kilometres north of Karachi.