By Sylvain Andzongo and Joel Kouam

YAOUNDE/ESEKA, Cameroon (Reuters) - Cameroon observed a day of mourning on Monday for victims of a deadly rail accident that has killed at least 75 people and exposed widespread frustration with one of Africa's longest-ruling presidents.

At the Eseka train station near where a packed passenger train carrying more than 1,300 people from Yaounde to the port of Douala derailed and flipped over last week, thousands of people gathered to mourn.

Many wore black and carried small branches from the local "peace tree" associated with sorrow during the inter-religious service where they sang religious hymns.

The official death toll from the accident is expected to rise further, with an unspecified number of unidentified bodies being kept in a Yaounde morgue, according to state television.

The work has been complicated by the fact there were no official lists of passengers since many did not have tickets.

"I still cannot find my brother who was on this train," said Arouna in Yaounde, who did not want to give his full name. "Nobody has been able to help me since Friday."

In Eseka, some residents said they had seen many more bodies than had been officially reported although this could not be independently verified. Around 600 people are still being treated for injuries and officials made urgent calls for blood donations to help those who still needed transfusions.

On the streets of the capital Yaounde, many openly criticized the reaction of President Paul Biya's government to an accident which they say should have been avoidable.

A train run by the same company, Camrail, a unit of French industrial group Bollore, also derailed in 2009 near Yaounde, killing five people and injuring more than 200.

"Many people are dead because they did not receive help that could have saved them at the right time," said Baudelaire Kemajou, a survivor of the crash who lost several friends in the accident and had to wait four hours for help.

A local travel agency sent cars to transport the injured before official help arrived, witnesses said.

Demand for tickets on the Camrail train had been especially high due to the collapse of a portion of a main highway on the same route and extra carriages were added at the last minute.

It is unclear whether this played a role in the crash.

INDIFFERENCE AT THE TOP?

Biya, who has ruled since 1982, arrived back in the country on Sunday afternoon after a 35-day absence following the U.N. General Assembly in New York and a "a private stay in Europe", according to his website.

While Biya is often absent for long periods, some expressed anger that he had not returned earlier to manage the crisis.

"Cameroonians are exasperated by his repeated shows of indifference during the tragedies of this country over the past 34 years," said Jean Michel Nintcheu, a member of parliament for the opposition Social Democratic Front.

Government officials have previously defended the absences, saying he does not need to be physically present to rule. Biya has called for an investigation into the crash and said the government would pay hospital fees for the injured.

Other Cameroonians said that his wife Chantal's decision to step off the plane wearing a bright pink suit jarred with the national mood of mourning.

"Her choice of clothes shows the disdain she has for the poor...She doesn't show her compassion," said Paulin, an economy ministry official who declined to give his full name.

However, Hans De Marie Heungoup, Cameroon analyst with International Crisis Group, said he doubted the incident would have major long-term political consequences for Biya.

"In Cameroonian politics there is practically no culture of accountability," he said, describing opposition to Biya as "fragile and fragmented".

(Additional reporting and writing by Emma Farge; editing by Mark Heinrich)