We are conducting an investigation right now

Director-general of the national police, Leandro Mendoza

State television said Mr Estrada invited 50 guests to a party at the hospital last month, where he reportedly handed out gifts and held a raffle.

The prizes were said to have included flights to Hong Kong, television sets and washing machines.

When the government found out, the security guards were replaced, the station reported.

"The old set of guards failed to observe procedure," said Interior Secretary Jose Lina. "They have already been removed and relieved and transferred to other assignments."

The director-general of the national police, Leandro Mendoza, said police were looking into the incident.

"This is a clear violation of specific instructions from my office and also from the court, so we are conducting an investigation right now," he said.

Perks curbed

Security has been stepped up and Mr Estrada is no longer allowed to use a mobile phone, Philippine radio reported.

Mr Estrada has recently had a cataract operation

The previous guards had allowed the former president to give personal interviews to journalists. But Mr Estrada's lawyer, Raymond Fortun, said that had now been curtailed, describing the move as "cruel".

Last month the Sandiganbayan anti-graft court hearing Mr Estrada's case turned down his request to spend Christmas at his suburban Manila mansion.

It has also rejected his request to be placed under house arrest.

Mr Estrada's presidency ended amid a military-backed popular uprising, which replaced him with President Gloria Arroyo.

The corruption trial began in October, but has faced frequent delays after a series of legal rows, including the sacking of judges.

The trial resumed on Monday following a three-week break. Mr Estrada, 64, has recently undergone eye surgery and was not in court.

In addition to the more serious plunder charge, Mr Estrada has also been charged with perjury and for illegally using an alias to hide his wealth.

Mr Estrada has denied all the charges against him, saying they are politically motivated.