The Federal Government is under increased pressure to hold a proper search for 160 missing boat people amid anger over the solitary search aircraft and claims by distraught relatives that Australia does not care.

It was also revealed yesterday that Australia's total contact with Indonesia's rescue authorities over the possible disaster has been one email asking for information, not help.

Late yesterday, the customs vessel Wauri was due to begin patrols around the Ashmore Islands off Western Australian, the apparent destination of the two rickety wooden boats filled with men, women and children.

Previously, a single Australian Dash-8 aircraft had been searching the vast area for any sign of the boats, believed to have set off from an island near Bali on December 5.

The vessels were possibly heading into cyclonic conditions.

It was revealed yesterday that the Indonesians had not yet replied to Wednesday's email, which made no request for permission to extend the search into Indonesian waters.

But a spokesman for the Indonesian Embassy, Mr Lutfi Rauf, confirmed that Jakarta's maritime safety agency had conducted boat searches from its Kupang base in Timor over the past two days without success.

A Sydney relative of a man on one of the boats said she believed that saving money was behind the reluctance of Australian authorities to do more.

'They're [not prepared to be] spending all this money on 160 people going missing ... because they don't want them here anyway,' she said. 'These people could be doctors or engineers [like my relative] they can make a contribution to this country.'

The Herald revealed yesterday that two Sydney mothers are waiting for their Iranian sons, who had told them they were leaving on a boat a week-and-a-half ago.

The Immigration Department was receiving more reports from relatives yesterday.

The Immigration Minister, Mr Ruddock, announced on Wednesday that the boats were missing and may have sunk.

Since then, thousands of square kilometres of ocean have been left uncovered by searchers, with a Coastwatch spokesman, Mr Leon Beddington, saying it was the responsibility of the Australian Maritime Safety Authority to call in defence aircraft to assist.

The solitary Dash-8 had done daily patrols from Broome to Darwin and along 'entry corridors' into Ashmore Islands, 800 kilometres north-west of Darwin.

The Opposition's acting customs spokesman, Mr Robert McClelland, said 'sending one Dash-8 ... can't be regarded as a proper response'.

'We have got to factor in it has obviously been a couple of days since the boats went down but obviously time's of the essence.'

When Mr Ruddock first announced the boats may have sunk, he said he had asked Coastwatch to increase efforts in the area and for the AMSA to 'attempt to locate any maritime reports of the incident'.

But a spokesman for Mr Ruddock said yesterday it was not in the minister's portfolio to direct that there be a formal search.

'It would come down to what information they [AMSA] would have on where they would search,' the spokesman said.

An AMSA spokesman, Mr David Gray, said of the email to Indonesia, sent on the international shipping system INMARSAT : 'We have requested if they have any information at all about this issue they obviously don't have information because they haven't come back to us.'

Japanese authorities have said there is no report of four survivors being picked up by a Japanese tanker as earlier claimed.