HAVANA -- Cuba's fuel shortages have increased dramatically with authorities suspending activities, including a concert by the country's national symphony, as well as rationing gasoline sales and moving some universities' classes online.

Cubans have experiences shortages of all kinds of goods amid the recent economic crisis but the cancellation of activities because of fuel shortages had not been reported previously. The cancellations come following days of long lines to get gasoline at filling stations.

Experts say the lack of gasoline and diesel is not due to a lack of crude oil -- Cuba produces about half of what it needs and buys the rest from other countries -- but to the difficulties refining it.

"There is no lack of crude oil in Cuba," said Jorge Pinon, senior research fellow at the University of Texas at Austin's Energy Institute.

He said Venezuela is selling Cuba a similar amount of crude or even slightly more than it did last year. Cuba has also received oil from Russia, though details of these agreements are unknown.

Pinon said Cuba in April also received two tankers from Mexican state oil company Pemex carrying 300,000 barrels of crude oil each.

He blamed he shortages on technical production problems in the refineries, which were built in 1957.

Cuban authorities have not given a specific reason for the shortages, but in previous days have mentioned difficulties with "inputs," which Pinon said could refer to an additive Cuba gets from Iran needed to refine Venezuela's heavy crude.

The fuel shortages started being critical this weekend.

On Monday afternoon, the commercial director of the state-owned Cubapetroleo, Lidia Rodriguez, warned there are low levels of "refineable crude."

Meanwhile, authorities in Villa Clara said in statement published on the government's Facebook page that fuel will only be sold to drivers of cars licensed to operate as public carriers and provide basic services, i.e. ambulances, and vehicles used in emergencies or burials.

Universities in the provinces of Villa Clara, Holguin, Sancti Spiritus and Universidad Agraria de La Habana said that starting Monday classes will be temporarily online.

On Sunday, a concert by the Cuban National Symphony in the capital's main theatre was cancelled due to lack of fuel.