CARACAS (Reuters) - President Nicolas Maduro's government is likely underestimating the number of Zika cases in Venezuela, which could hurt efforts to combat the virus-bearing mosquito, according to local doctors, opposition politicians and neighbouring Colombia.

Some 4,700 cases of suspected Zika have been reported in the hot and humid country, Venezuela's Health Minister Luisana Melo said last week in the first official estimate of the virus, which has been linked to severe birth defects in thousands of babies in Brazil.

The ministry stopped issuing weekly health bulletins over a year ago, meaning there is no public historical data or geographic statistics for unusual fever outbreaks.

Alarmed doctors say Venezuela, which is mired in economic crisis and has chronic shortages of products ranging from fever relievers to repellent, actually has far a greater incidence of Zika.

The number of cases could range between 240,000 and 500,000, according to infectious disease specialist Julio Castro, who bases his estimates on algorithmic projections and leaked health bulletins.

"The government is hiding information," said Jose Manuel Olivares, a radiation oncologist and newly-elected opposition lawmaker who works closely with Castro.

A Health Ministry spokesman was not immediately available for comment.

Complicating efforts in any country to get a handle on numbers, some 80 percent of people who contract Zika show no symptoms.

Olivares said the official estimate of around 255 cases of Guillain-Barré, an autoimmune syndrome that can cause paralysis, was a further indication of Zika's spread in Venezuela. Like the birth defect known as microcephaly, Guillain-Barré is suspected to be linked with Zika, although the connection is not yet definitive.

"If the government doesn't recognise the magnitude of the crisis it won't act on it. The number of Zika cases is going to increase," added Olivares, president of the congressional health commission.

NO REPELLENT, LOTS OF TRASH

Scarcity of condoms and birth control pills have contributed to unwanted pregnancies in Venezuela, where abortion is illegal unless a woman's health is at risk and teenage pregnancy rates are high. The fight against Zika is complicated by repellent shortages and uncollected trash.

Shortages might also hinder diagnosis of Zika and possible associated problems.

Colombia, whose center-right government often clashes with Socialist-run Caracas, said on Monday the cases of Guillain-Barré reported in Venezuela suggested it had far more cases of Zika.

"The Zika situation in Venezuela might be much more serious than in our country," Health Minister Alejandro Gaviria told BLU Radio.

Colombia on Saturday reported 20,297 confirmed Zika cases, with 2,116 of them pregnant women.

(Editing by Brian Ellsworth and Frances Kerry)