Evacuation centres open as cyclone Seroja intensifies off Western Australia

The cyclone was rapidly moving south east but was likely to weaken to category 2 in severity prior to making landfall later in the evening, the Bureau of Meteorology said.

Tropical cyclone Seroja strengthened off Western Australia on Sunday, with emergency services broadening a warning to immediately take shelter to several towns given high winds and the prospect of coastal flooding.

Multiple disasters triggered by Tropical Cyclone Seroja in eastern Indonesia East Timor have left a number of people dead or missing. (AP)

Five coastal towns were put on red alert by Sunday afternoon, including residents in Denham, Shark Bay, 500 kilometres (311 miles) north of Perth, while sandbags were made available to those in Geraldton, further down the coast, due to potential storm surge.

"There is a threat to lives and homes. You are in danger and need to act immediately," the Department of Fire and Emergency Services (DFES) said in a bulletin.

The cyclone, which was upgraded in severity to category 3 on Sunday, was rapidly moving south east but was likely to weaken to category 2 in severity prior to making landfall later in the evening, the Bureau of Meteorology said. Wind gusts of 150 kilometres an hour were expected.

Officials were braced for a high degree of damage to towns along the coast, the state emergency services minister said on Saturday, given buildings were not constructed to withstand such strong winds in a region that is typically too far south to fall into the path of cyclones.