Singapore on Sunday deported 29 mainland Chinese bus drivers involved in the city-state's first industrial strike in 26 years.

The drivers, working for state-linked transport operator SMRT, staged the strike on Monday and Tuesday over a salary dispute and to demand better working conditions. Their work permits had been revoked ahead of their deportation.

"The Ministry of Home Affairs confirms that all 29 former SMRT bus drivers have been repatriated to their home country," the ministry said in a statement.

"They were cooperative and the process took place without incident," it said, adding that Chinese embassy officials and SMRT staff assisted in the repatriation.

Four other drivers were charged in court and authorities said they would lodge charges against a fifth on Monday for their involvement in the work stoppage which the government ruled was illegal.

If found guilty, they could be jailed for up to a year, fined a maximum of Sg$2,000 ($1,640) -- the equivalent of two months' wages -- or both.

The strike, the first since 1986 and which caught the government by surprise, has highlighted tightly-controlled Singapore's heavy dependency on migrant labour to drive its economic growth amid a labour shortage resulting from falling birth rates.

Strikes are illegal in the affluent island-state for workers in "essential services" such as transport unless they give 14 days' prior notice and meet other requirements.

Manpower Minister Tan Chuan-Jin said Saturday the workers broke Singapore law, but also chided SMRT saying the company "could have done better in managing their labour grievances and concerns".

SMRT has promised to look into the strikers' demands, fumigate their bedbug-infested dormitory rooms, find alternative housing in 2013 and open permanent communication lines with its Chinese workers.

"Valuable lessons have been learnt from this incident which are being addressed by the management," SMRT said in a statement Saturday, pledging to be "more proactive, responsible and sensitive to the needs" of its drivers.

A total of 171 drivers launched the strike November 26 by refusing to report for work and staying in their dormitories, with the number falling to 88 on the second day.

Sinapan Samydorai, director for Southeast Asian affairs at civil rights group Think Centre, on Saturday criticised the government action as "a bit too harsh".